High density memory device

ABSTRACT

This invention provides novel high density memory devices that are electrically addressable permitting effective reading and writing, that provide a high memory density (e.g., 10 15  bits/cm 3 ), that provide a high degree of fault tolerance, and that are amenable to efficient chemical synthesis and chip fabrication. The devices are intrinsically latchable, defect tolerant, and support destructive or non-destructive read cycles. In a preferred embodiment, the device comprises a fixed electrode electrically coupled to a storage medium having a multiplicity of different and distinguishable oxidation states wherein data is stored in said oxidation states by the addition or withdrawal of one or more electrons from said storage medium via the electrically coupled electrode.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. Ser. No. 10/019,377, which isa 371 of PCT/US00/17847, filed on Jun. 28, 2000, which is aContinuation-in-Part of U.S. Ser. No. 09/346,221, filed on Jul. 1, 1999,now U.S. Pat. No. 6,208,553, and is a Continuation-in-Part of U.S. Ser.No. 09/346,228, filed on Jul. 1, 1999, now U.S. Pat. No. 6,381,169, andU.S. Ser. No. 09/484,394, filed on Jan. 14, 2000, now U.S. Pat. No.6,324,091, all of which are incorporated herein by reference in theirentirety for all purposes.

STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSOREDRESEARCH AND DEVELOPMENT

This invention was made with government support under Grant NumberN00014-99-1-0357 from the Office of Naval Research. The Government ofthe United States of America may have certain rights in the invention.

FIELD OF THE INVENTION

This invention relates to memory devices. In particular this inventionprovides a nonvolatile electronic memory device capable of storinginformation in extremely high density.

BACKGROUND OF THE INVENTION

Basic functions of a computer include information processing andstorage. In typical computer systems, these arithmetic, logic, andmemory operations are performed by devices that are capable ofreversibly switching between two states often referred to as “0” and“1.” In most cases, such switching devices are fabricated fromsemiconducting devices that perform these various functions and arecapable of switching between two states at a very high speed usingminimum amounts of electrical energy. Thus, for example, transistors andtransistor variants perform the basic switching and storage functions incomputers.

Because of the huge data storage requirements of modern computers, anew, compact, low-cost, very high capacity, high speed memoryconfiguration is needed. To reach this objective, molecular electronicswitches, wires, microsensors for chemical analysis, and opto-electroniccomponents for use in optical computing have been pursued. The principaladvantages of using molecules in these applications are high componentdensity (upwards of 10¹⁸ bits per square centimeter), increased responsespeeds, and high energy efficiency.

A variety of approaches have been proposed for molecular-based memorydevices. While these approaches generally employ molecular architecturesthat can be switched between two different states, all of the approachesdescribed to date have intrinsic limitations making their uses incomputational devices difficult or impractical.

For example, such approaches to the production of molecular memorieshave involved photochromic dyes, electrochromic dyes, redox dyes, andmolecular machines. Each of these approaches, however, has intrinsiclimitations that ultimately render it unsuitable for use in molecularmemories. For example, photochromic dyes change conformation in responseto the absorption of light (e.g. cis-trans interconversion of an alkene,ring opening of a spiropyran, interconversion between excited-states inbacteriorhodopsin, etc.). Typically, the molecular structure of the dyeis interconverted between two states that have distinct spectralproperties.

Reading and writing data with such photochromic dyes requires use oflight, often in the visible region (400-700 nm). Light-mediated datastorage has intrinsic diffraction-limited size constraints. Moreover,most photochromic schemes are limited to scanning and interrogating dyesdeposited on a surface and are not amenable to 3-D data storage. Evenwith near-field optical approaches, which might allow reliableencoding/reading of data elements of 100×100 nm dimensions(Nieto-Vesperinas and Garcia, N., eds. (1996) Optics at the NanometerScale, NATO ASI Series E, Vol. 319, Kluwer Academic Publishers:Dordrecht) the inherent restricted dimensionality (2-D) limits datadensity to 10¹⁰ bits/cm². Strategies for 3-dimensional reading andwriting of photochromic systems have been proposed that rely ontwo-photon excitation of dyes to encode data, and one-photon excitationto read the data (Birge et al. (1994) Amer. Sci. 82: 349-355,Parthenopoulos and Rentzepis (1989) Science, 245: 843-845), but it isbelieved that no high-density memory cubes have reached prototype stagein spite of the passage of at least a decade since their initialproposition. In addition, it is noted that these dyes often exhibitrelatively slow switching times ranging from microsecond to milliseconddurations.

Electrochromic dyes have been developed that undergo a slight change inabsorption spectrum upon application of an applied electric field(Liptay (1969) Angew. Chem., Int. Ed. Engl. 8: 177-188). The dyes mustbe oriented in a fixed direction with respect to the applied field.Quite high fields (>10⁷ V/cm) must be applied to observe an alteredabsorption spectrum which can result in heat/power dissipation problems.In addition, the change in the absorption spectrum is typically quitesmall, which can present detection difficulties. The dyes revert to theinitial state when the applied field is turned off.

Redox dyes have been developed that undergo a change in absorptionspectrum upon chemical or electrochemical reduction (typically a2-electron, 2-proton reduction) (Otsuki et al. (1996) Chem. Lett.847-848). Such systems afford bistable states (e.g.,quinone/hydroquinone, azo/hydrazo). Redox dyes have only been examinedin solution studies, where they have been proposed for applications asswitches and sensors (de Silva et al. (1997) Chem. Rev. 97: 1515-1566).On a solid substrate, electrochemical reduction would need to beaccompanied by a source of protons. The latter requirement may bedifficult to achieve on a solid substrate. Furthermore, any opticalreading scheme would pose the same 2-D limitations as described forphotochromic dyes.

Yet another approach involves the design of molecular machines (Anell etal. (1992) J. Am. Chem. Soc. 114: 193-218). These elegant moleculararchitectures have moving parts that can be switched from one positionto another by chemical or photochemical means. The chemically inducedsystems have applications as sensors but are not practical for memorystorage, while the photochemically induced systems have the samefundamental limitations as photochromic dyes. Moreover, methods have notyet been developed for delineating the conformation/structure of themolecular machine that are practical in any device applications. ¹H NMRspectroscopy, for example, is clearly the method of choice forelucidating structure/conformation for molecules in solution, but istotally impractical for interrogating a molecular memory element. Noneof the current architectures for molecular machines has been designedfor assembly on a solid substrate, an essential requirement in a viabledevice.

In summary, photochromic dyes, electrochromic dyes, redox-sensitivedyes, and molecular machines all have fundamental limitations that haveprecluded their application as viable memory elements. These moleculararchitectures are typically limited by reading/writing constraints.Furthermore, even in cases where the effective molecular bistability isobtained, the requirement for photochemical reading restricts the devicearchitecture to a 2-dimensional thin film. The achievable memory densityof such a film is unlikely to exceed 10¹⁰ bits/cm². Such limitationsgreatly diminish the appeal of these devices as viable molecular memoryelements.

SUMMARY OF THE INVENTION

This invention provides novel high density memory devices that areelectrically addressable permitting effective reading and writing, thatprovide a high memory density (e.g., 10¹⁵ bits/cm³), that provide a highdegree of fault tolerance, and that are amenable to efficient chemicalsynthesis and chip fabrication. The devices are intrinsically latchable,defect tolerant, and support destructive or non-destructive read cycles.

In a preferred embodiment, this invention provides an apparatus forstoring data (e.g., a “storage cell”). The storage cell includes a fixedelectrode electrically coupled to a “storage medium” having amultiplicity of different and distinguishable oxidation states wheredata is stored in the (preferably non-neutral) oxidation states by theaddition or withdrawal of one or more electrons from said storage mediumvia the electrically coupled electrode. In preferred storage cells, thestorage medium stores data at a density of at least one bit, preferablyat a density of at least 2 bits, more preferably at a density of atleast 3 bits, and most preferably at a density of at least 5, 8, 16, 32,or 64 bits per molecule. Thus, preferred storage media have at least 2,8, 16, 32, 64, 128 or 256 different and distinguishable oxidationstates. In particularly preferred embodiments, the bits are all storedin non-neutral oxidation states. In a most preferred embodiment, thedifferent and distinguishable oxidation states of the storage medium canbe set by a voltage difference no greater than about 5 volts, morepreferably no greater than about 2 volts, and most preferably no greaterthan about 1 volt.

The storage medium is electrically coupled to the electrode(s) by any ofa number of convenient methods including, but not limited to, covalentlinkage (direct or through a linker), ionic linkage, non-ionic“bonding”, simple juxtaposition/apposition of the storage medium to theelectrode(s), or simple proximity to the electrode(s) such that electrontunneling between the medium and the electrode(s) can occur. The storagemedium can contain or be juxtaposed to or layered with one or moredielectric material(s). Preferred dielectric materials are imbedded withcounterions (e.g. Nafion). The storage cells of this invention are fullyamenable to encapsulation (or other packaging) and can be provided in anumber of forms including, but not limited to, an integrated circuit oras a component of an integrated circuit, a non-encapsulated “chip”, etc.In some embodiments, the storage medium is electronically coupled to asecond electrode that is a reference electrode. In certain preferredembodiments, the storage medium is present in a single plane in thedevice. The apparatus of this invention can include the storage mediumpresent at a multiplicity of storage locations, and in certainconfigurations, each storage location and associated electrode(s) formsa separate storage cell. The storage present on a single plane in thedevice or on multiple planes and said storage locations are present onmultiple planes of said device. Virtually any number (e.g., 16, 32, 64,128, 512, 1024, 4096, etc.) of storage locations and/or storage cellscan be provided in the device. Each storage location can be addressed bya single electrode or by two or more electrodes. In other embodiments, asingle electrode can address multiple storage locations and/or multiplestorage cells.

In preferred embodiments, one or more of the electrode(s) is connectedto a voltage source (e.g. output of an integrated circuit, power supply,potentiostat, microprocessor (CPU), etc.) that can provide avoltage/signal for writing, reading, or refreshing the storage cell(s).One or more of the electrode(s) is preferably connected to a device(e.g., a voltammetric device, an amperometric device, a potentiometricdevice, etc.) to read the oxidation state of said storage medium. Inparticularly preferred embodiments, the device is an impedancespectrometer or a sinusoidal voltammeter. Various signal processingmethods can be provided to facilitate readout in the time domain or inthe frequency domain. Thus, in some embodiments, the readout device(s)provide a Fourier transform (or other frequency analysis) of the outputsignal from said electrode. In certain preferred embodiments, the devicerefreshes the oxidation state of said storage medium after reading saidoxidation state.

In order to simplify construction of the arrays for molecular basedinformation storage, in certain embodiments, this invention describesthe use of polymeric molecules having multiple oxidation states wherethe monomeric subunits comprising the polymers are tightly coupled (e.g.directly linked as opposed to linking through a linker). The “tightcoupling” is manifested as a splitting in redox potentials of thestructurally identical subunits. Thus, for example, combination of twoidentical subunits each having two identical non-zero oxidation statescan result in a dimer having four different and distinguishable non-zerooxidation states. This greatly simplifies fabrication of a storagemolecule as, in this instance, only a single type of subunit need besynthesized. Thus, in one embodiment, this invention provides anapparatus for storing data comprising a fixed electrode electricallycoupled to a storage medium comprising a storage molecule having a firstsubunit and a second subunit (i.e. at least two subunits) wherein thefirst and second subunits are tightly coupled such that oxidation of thefirst subunit alters the oxidation potential of the second subunit.

A wide variety of molecules can be used as storage molecules and hencecomprise the storage medium. Preferred molecules include, but are notlimited to a porphyrinic macrocycle, a metallocene, a linear polyene, acyclic polyene, a heteroatom-substituted linear polyene, aheteroatom-substituted cyclic polyene, a tetrathiafulvalene, atetraselenafulvalene, a metal coordination complex, a buckyball, atriarylamine, a 1,4-phenylenediamine, a xanthene, a flavin, a phenazine,a phenothiazine, an acridine, a quinoline, a 2,2′-bipyridyl, a4,4′-bipyridyl, a tetrathiotetracene, and a peri-bridged naphthalenedichalcogenide. Even more preferred molecules include a porphyrin, anexpanded porphyrin, a contracted porphyrin, a ferrocene, a linearporphyrin polymer, and a porphyrin array. Certain particularly preferredstorage molecules include a porphyrinic macrocycle substituted at aβ-position or at a meso-position. Molecules well suited for use asstorage molecules include the molecules described herein (e.g. themolecules of Formulas I-XXXIV).

The storage molecule can be directly covalently linked to the electrodeor covalently linked through a linker (see, e.g., FIG. 34). In anotherembodiment, the storage medium is juxtaposed in the proximity of saidelectrode such that electrons can pass from said storage medium to saidelectrode. The storage medium can be juxtaposed to (or embedded in) adielectric material imbedded with counterions. In some embodiments, thestorage medium and said electrode are fully encapsulated in anintegrated circuit. The storage medium can be electronically coupled toa second fixed electrode that is a reference electrode. In onearchitecture, the storage medium is present on a single plane in saiddevice, while in another architecture, the storage medium is present ata multiplicity of storage locations. The apparatus may comprise multipleplanes and the storage locations may be present on multiple planes ofthe device. In preferred devices, the storage locations range from about1024 to about 4096 different locations. Each location can be addressedby a single electrode or each location can be addressed by two (or more)electrodes. Typically at least one electrode is connected to a voltagesource (e.g. the output of an integrated circuit).

Typically at least one electrode is connected to a device (e.g. avoltammetric device, an amperometric device, or a potentiometric device)to read the oxidation state of the storage medium. Preferred devicesinclude, but are not limited to an impedance spectrometer or asinusoidal voltammeter. The device can optionally provide a Fouriertransform of the output signal from the electrode. The device can alsooptionally refresh the oxidation state of said storage medium afterreading the oxidation state.

Particularly preferred methods and/or devices of this invention utilizea “fixed” electrode. Thus, in one embodiment, methods and/or devices inwhich the electrode(s) are moveable (e.g. one or ore electrodes is a“recording head”, the tip of a scanning tunneling microscope (STM), thetip of an atomic force microscope (AFM), or other forms in which theelectrode is movable with respect to the storage medium are excluded. Incertain embodiments, methods and/or devices and/or storage media, and/orstorage molecules in which the storage molecule is analkanethiolferrocene are excluded. Similarly in certain embodiments,methods and/or devices and/or storage media, in which the storagemolecules are responsive to light and/or in which the oxidation state ofa storage molecule is set by exposure to light are excluded.

In another embodiment, this invention provides an information storagemedium. The information storage medium can be used to assemble storagecells and/or the various memory devices described herein. In a preferredembodiment the storage medium comprises one or more different storagemolecules. When different species of storage molecule are present, eachspecies of storage molecule oxidation state(s) different from anddistinguishable from the oxidation state(s) of the other species ofstorage molecule comprising the storage medium. In preferredembodiments, the storage molecule(s) include a porphyrinic macrocycle, ametallocene, a linear polyene, a cyclic polyene, aheteroatom-substituted linear polyene, a heteroatom-substituted cyclicpolyene, a tetrathiafulvalene, a tetraselenafulvalene, a metalcoordination complex, a buckyball, a triarylamine, a1,4-phenylenediamine, a xanthene, a flavin, a phenazine, aphenothiazine, an acridine, a quinoline, a 2,2′-bipyridyl, a4,4′-bipyridyl, a tetrathiotetracene, or a peri-bridged naphthalenedichalcogenide. In even more preferred embodiment, the storagemolecule(s) include a porphyrin, an expanded porphyrin, a contractedporphyrin, a ferrocene, a linear porphyrin polymer, or a porphyrinarray. Preferred storage molecules contain two or more covalently linkedredox-active subunits. In various preferred embodiments, the storagemolecules include any of the storage molecules as described herein (e.g.the molecules of Formulas I-XXXIV).

In still another embodiment this invention provides a collection ofmolecules for the production of a data storage medium. A preferredcollection comprises a plurality of storage molecules wherein eachspecies of storage molecule has an oxidation state different from anddistinguishable from the oxidation states of the other species ofstorage molecules comprising the collection. In various preferredembodiments, the storage molecules include any of the storage moleculesas described herein (e.g. the molecules of Formulas I-XXXIV).

This invention also provides particularly preferred molecules for thestorage of information (storage molecules). The molecules preferablyhave at least one non-neutral oxidation state and more preferably haveat least two different and distinguishable non-neutral oxidation states.In various preferred embodiments, the storage molecules include any ofthe storage molecules as described herein (e.g. the molecules ofFormulas I-XXXIV).

This invention also provides methods of storing data. The methodsinvolve i) providing an apparatus, e.g., comprising one or more storagecells as described herein; and ii) applying a voltage to the electrodeat sufficient current to set an oxidation state of said storage medium(the storage medium comprising one or more storage cells). In preferredembodiments, the voltage ranges is less than about 5 volts, morepreferably less than about 2 volts, and most preferably less than about1 or less than about 0.5 volts. The voltage can be the output of anyconvenient voltage source (e.g. output of an integrated circuit, powersupply, logic gate, potentiostat, microprocessor (CPU), etc.) that canprovide a voltage/signal for writing, reading, or refreshing the storagecell(s).

The method can further involve detecting the oxidation state of thestorage medium and thereby reading out the data stored therein. Thedetection (read) can optionally involve refreshing the oxidation stateof the storage medium (particularly in static-hole devices). The read(detecting) can involve analyzing a readout signal in the time orfrequency domain and can thus involve performing a Fourier transform onthe readout signal. The detection can be by any of a variety of methodsincluding, but not limited to a voltammetric method. One particularlypreferred readout utilizes impedance spectroscopy. The readout(detecting) can involve exposing the storage medium to an electric fieldto produce an electric field oscillation having characteristic frequencyand detecting the characteristic frequency. In preferred embodiments,the storage cells used in the methods of this invention have storagemedia comprising one or more of the storage molecules described herein(e.g. the molecules of Formulas I-XXXIV).

This invention additionally provides the memory devices of thisinvention (e.g. memory cells) in a computer system. In addition computersystems utilizing the memory devices of this invention are provided.Preferred computer systems include a central processing unit, a display,a selector device, and a memory device the storage devices (e.g. storagecells) of this invention.

Definitions

The term “oxidation” refers to the loss of one or more electrons in anelement, compound, or chemical substituent/subunit. In an oxidationreaction, electrons are lost by atoms of the element(s) involved in thereaction. The charge on these atoms must then become more positive. Theelectrons are lost from the species undergoing oxidation and soelectrons appear as products in an oxidation reaction. An oxidation istaking place in the reaction Fe²⁺(aq)- ->Fe³⁺(aq)+e⁻ because electronsare lost from the species being oxidized, Fe²⁺(aq), despite the apparentproduction of electrons as “free” entities in oxidation reactions.Conversely the term reduction refers to the gain of one or moreelectrons by an element, compound, or chemical substituent/subunit.

An “oxidation state” refers to the electrically neutral state or to thestate produced by the gain or loss of electrons to an element, compound,or chemical substituent/subunit. In a preferred embodiment, the term“oxidation state” refers to states including the neutral state and anystate other than a neutral state caused by the gain or loss of electrons(reduction or oxidation).

The term “multiple oxidation states” means more than one oxidationstate. In preferred embodiments, the oxidation states may reflect thegain of electrons (reduction) or the loss of electrons (oxidation).

The terms “different and distinguishable” when referring to two or moreoxidation states means that the net charge on the entity (atom,molecule, aggregate, subunit, etc.) can exist in two different states.The states are said to be “distinguishable” when the difference betweenthe states is greater than thermal energy at room temperature (e.g. 0°C. to about 40° C.).

The term “tightly coupled” when used in reference to a subunit of amulti-subunit (e.g., polymeric) storage molecule of this inventionrefers to positioning of the subunits relative to each other such thatoxidation of one subunit alters the oxidation potential(s) of the othersubunit. In a preferred embodiment the alteration is sufficient suchthat the (non-neutral) oxidation state(s) of the second subunit aredifferent and distinguishable from the non-neutral oxidation states ofthe first subunit. In a preferred embodiment the tight coupling isachieved by a covalent bond (e.g. single, double, triple, etc.).However, in certain embodiments, the tight coupling can be through alinker, via an ionic interaction, via a hydrophobic interaction, throughcoordination of a metal, or by simple mechanical juxtaposition. It isunderstood that the subunits could be so tightly coupled that the redoxprocesses are those of a single supermolecule.

The term “electrode” refers to any medium capable of transporting charge(e.g. electrons) to and/or from a storage molecule. Preferred electrodesare metals or conductive organic molecules. The electrodes can bemanufactured to virtually any 2-dimensional or 3-dimensional shape (e.g.discrete lines, pads, planes, spheres, cylinders, etc.).

The term “fixed electrode” is intended to reflect the fact that theelectrode is essentially stable and unmovable with respect to thestorage medium. That is, the electrode and storage medium are arrangedin an essentially fixed geometric relationship with each other. It is ofcourse recognized that the relationship alters somewhat due to expansionand contraction of the medium with thermal changes or due to changes inconformation of the molecules comprising the electrode and/or thestorage medium. Nevertheless, the overall spatial arrangement remainsessentially invariant. In a preferred embodiment this term is intendedto exclude systems in which the electrode is a movable “probe” (e.g. awriting or recording “head”, an atomic force microscope (AFM) tip, ascanning tunneling microscope (STM) tip, etc.).

The term “working electrode” is used to refer to one or more electrodesthat are used to set or read the state of a storage medium and/orstorage molecule.

The term “reference electrode” is used to refer to one or moreelectrodes that provide a reference (e.g. a particular referencevoltage) for measurements recorded from the working electrode. Inpreferred embodiments, the reference electrodes in a memory device ofthis invention are at the same potential although in some embodimentsthis need not be the case.

The term “electrically coupled” when used with reference to a storagemolecule and/or storage medium and electrode refers to an associationbetween that storage medium or molecule and the electrode such thatelectrons move from the storage medium/molecule to the electrode or fromthe electrode to the storage medium/molecule and thereby alter theoxidation state of the storage medium/molecule. Electrical coupling caninclude direct covalent linkage between the storage medium/molecule andthe electrode, indirect covalent coupling (e.g. via a linker), direct orindirect ionic bonding between the storage medium/molecule and theelectrode, or other bonding (e.g. hydrophobic bonding). In addition, noactual bonding may be required and the storage medium/molecule maysimply be contacted with the electrode surface. There also need notnecessarily be any contact between the electrode and the storagemedium/molecule where the electrode is sufficiently close to the storagemedium/molecule to permit electron tunneling between the medium/moleculeand the electrode.

The term “redox-active unit” or “redox-active subunit” refers to amolecule or component of a molecule that is capable of being oxidized orreduced by the application of a suitable voltage.

The term “subunit”, as used herein, refers to a redox-active componentof a molecule.

The terms “storage molecule” or “memory molecule” refer to a moleculehaving one or more oxidation states that can be used for the storage ofinformation (e.g. a molecule comprising one or more redox-activesubunits). Preferred storage molecules have two or more different anddistinguishable non-neutral oxidation states.

The term “storage medium” refers to a composition comprising two or morestorage molecules. The storage medium can contain only one species ofstorage molecule or it can contain two or more different species ofstorage molecule. In preferred embodiments, the term “storage medium”refers to a collection of storage molecules. Preferred storage mediacomprise a multiplicity (at least 2) of different and distinguishable(preferably non-neutral) oxidation states. The multiplicity of differentand distinguishable oxidation states can be produced by the combinationof different species of storage molecules, each species contributing tosaid multiplicity of different oxidation states and each species havinga single non-neutral oxidation state. Alternatively or in addition, thestorage medium can comprise one or more species of storage moleculehaving a multiplicity of non-neutral oxidation states. The storagemedium can contain predominantly one species of storage molecule or itcan contain a number of different storage molecules. The storage mediacan also include molecules other than storage molecules (e.g. to providechemical stability, suitable mechanical properties, to prevent chargeleakage, etc.).

The term “electrochemical cell” consists minimally of a referenceelectrode, a working electrode, a redox-active medium (e.g. a storagemedium), and, if necessary, some means (e.g., a dielectric) forproviding electrical conductivity between the electrodes and/or betweenthe electrodes and the medium. In some embodiments, the dielectric is acomponent of the storage medium.

The terms “memory element”, “memory cell”, or “storage cell” refer to anelectrochemical cell that can be used for the storage of information.Preferred “storage cells” are discrete regions of storage mediumaddressed by at least one and preferably by two electrodes (e.g. aworking electrode and a reference electrode). The storage cells can beindividually addressed (e.g. a unique electrode is associated with eachmemory element) or, particularly where the oxidation states of differentmemory elements are distinguishable, multiple memory elements can beaddressed by a single electrode. The memory element can optionallyinclude a dielectric (e.g. a dielectric impregnated with counterions).

The term “storage location” refers to a discrete domain or area in whicha storage medium is disposed. When addressed with one or moreelectrodes, the storage location may form a storage cell. However if twostorage locations contain the same storage media so that they haveessentially the same oxidation states, and both storage locations arecommonly addressed, they may form one functional storage cell.

“Addressing” a particular element refers to associating (e.g.,electrically coupling) that memory element with an electrode such thatthe electrode can be used to specifically determine the oxidationstate(s) of that memory element.

The term “storage density” refers to the number of bits per volumeand/or bits per molecule that can be stored. When the storage medium issaid to have a storage density greater than one bit per molecule, thisrefers to the fact that a storage medium preferably comprises moleculeswherein a single molecule is capable of storing at least one bit ofinformation.

The terms “read” or “interrogate” refer to the determination of theoxidation state(s) of one or more molecules (e.g. molecules comprising astorage medium).

The term “refresh” when used in reference to a storage molecule or to astorage medium refers to the application of a voltage to the storagemolecule or storage medium to re-set the oxidation state of that storagemolecule or storage medium to a predetermined state (e.g. an oxidationstate the storage molecule or storage medium was in immediately prior toa read).

The term “E_(1/2)” refers to the practical definition of the formalpotential (E^(o)) of a redox process as defined byE=E^(o)+(RT/nF)ln(D_(ox)/D_(red)) where R is the gas constant, T istemperature in K (Kelvin), n is the number of electrons involved in theprocess, F is the Faraday constant (96,485 Coulomb/mole), D_(ox) is thediffusion coefficient of the oxidized species and D_(red) is thediffusion coefficient of the reduced species.

A “voltage source” is any source (e.g. molecule, device, circuit, etc.)capable of applying a voltage to a target (e.g. an electrode).

The term “present on a single plane”, when used in reference to a memorydevice of this invention refers to the fact that the component(s) (e.g.storage medium, electrode(s), etc.) in question are present on the samephysical plane in the device (e.g. are present on a single lamina).Components that are on the same plane can typically be fabricated at thesame time, e.g., in a single operation. Thus, for example, all of theelectrodes on a single plane can typically be applied in a single (e.g.,sputtering) step (assuming they are all of the same material).

The phrase “output of an integrated circuit” refers to a voltage orsignal produced by a one or more integrated circuit(s) and/or one ormore components of an integrated circuit.

A “voltammetric device” is a device capable of measuring the currentproduced in an electrochemical cell as a result of the application of avoltage or change in voltage.

An “amperometric device” is a device capable of measuring the currentproduced in an electrochemical cell as a result of the application of aspecific potential field potential (“voltage”).

A “potentiometric device” is a device capable of measuring potentialacross an interface that results from a difference in the equilibriumconcentrations of redox molecules in an electrochemical cell.

A “coulometric device” is a device capable of the net charge producedduring the application of a potential field (“voltage”) to anelectrochemical cell.

An “impedance spectrometer” is a device capable of determining theoverall impedance of an electrochemical cell.

A “sinusoidal voltammeter” is a voltammetric device capable ofdetermining the frequency domain properties of an electrochemical cell.

The term “porphyrinic macrocycle” refers to a porphyrin or porphyrinderivative. Such derivatives include porphyrins with extra ringsortho-fused, or ortho-perifused, to the porphyrin nucleus, porphyrinshaving a replacement of one or more carbon atoms of the porphyrin ringby an atom of another element (skeletal replacement), derivatives havinga replacement of a nitrogen atom of the porphyrin ring by an atom ofanother element (skeletal replacement of nitrogen), derivatives havingsubstituents other than hydrogen located at the peripheral (meso-, β-)or core atoms of the porphyrin, derivatives with saturation of one ormore bonds of the porphyrin (hydroporphyrins, e.g., chlorins,bacteriochlorins, isobacteriochlorins, decahydroporphyrins, corphins,pyrrocorphins, etc.), derivatives obtained by coordination of one ormore metals to one or more porphyrin atoms (metalloporphyrins),derivatives having one or more atoms, including pyrrolic andpyrromethenyl units, inserted in the porphyrin ring (expandedporphyrins), derivatives having one or more groups removed from theporphyrin ring (contracted porphyrins, e.g., corrin, corrole) andcombinations of the foregoing derivatives (e.g. phthalocyanines,sub-phthalocyanines, and porphyrin isomers). Preferred porphyrinicmacrocycles comprise at least one 5-membered ring.

The term “porphyrin” refers to a cyclic structure typically composed offour pyrrole rings together with four nitrogen atoms and two replaceablehydrogens for which various metal atoms can readily be substituted. Atypical porphyrin is hemin.

The term “multiporphyrin array” refers to a discrete number of two ormore covalently-linked porphyrinic macrocycles. The multiporphyrinarrays can be linear, cyclic, or branched.

A “linker” is a molecule used to couple two different molecules, twosubunits of a molecule, or a molecule to a substrate.

A “substrate” is a, preferably solid, material suitable for theattachment of one or more molecules. Substrates can be formed ofmaterials including, but not limited to glass, plastic, silicon,minerals (e.g. quartz), semiconducting materials, ceramics, metals, etc.

The term “odd hole oxidation state”, refers to the case where the numberof electron equivalents added or removed from a molecule or molecules isnot an integer multiple of the number of redox-active (e.g. oxidizableor reducable) subunits in the molecule or molecules.

The phrase “hole hopping” refers to the exchange of oxidation statesbetween subunits of thermodynamically similar potentials.

The term “aryl” refers to a compound whose molecules have the ringstructure characteristic of benzene, naphthalene, phenanthrene,anthracene, etc. (i.e., either the 6-carbon ring of benzene or thecondensed 6-carbon rings of the other aromatic derivatives). Forexample, and aryl group may be phenyl (C₆H₃) or naphthyl (C₁₀H₉). It isrecognized that the aryl, while acting as substituent can itself haveadditional substituents (e.g. the substituents provided for S^(n) in thevarious Formulas herein).

The term “alkyl” refers to a paraffinic hydrocarbon group which may bederived from an alkane by dropping one hydrogen from the formula.Examples are methyl (CH₃—), ethyl (C₂H₅—), propyl (CH₃CH₂CH₂—),isopropyl ((CH₃)₂CH₃—).

The term “halogen” refers to one or the electronegative elements ofgroup VIIA of the periodic table (fluorine, chlorine, bromine, iodine,astatine).

The term “nitro” refers to the NO₂ group.

The term “amino” refers to the NH₂ group.

The term “perfluoroalkyl” refers to an alkyl group where every hydrogenatom is replaced with a fluorine atom.

The term “perfluoroaryl” refers to an aryl group where every hydrogenatom is replaced with a fluorine atom.

The term “pyridyl” refers to an aryl group where one CH unit is replacedwith a nitrogen atom.

The term “cyano” refers to the —CN group.

The term “thiocyanato” refers to the —SCN group.

The term “sulfoxyl” refers to a group of composition RS(O)— where R issome alkyl, aryl, cycloalkyl, perfluoroalkyl, or perfluoroaryl group.Examples include, but are not limited to methylsulfoxyl, phenylsulfoxyl,etc.

The term “sulfonyl” refers to a group of composition RSO₂— where R issome alkyl, aryl, cycloalkyl, perfluoroalkyl, or perfluoroaryl group.Examples include, but are not limited to methylsulfonyl, phenylsulfonyl,p-toluenesulfonyl, etc.

The term “carbamoyl” refers to the group of composition R¹(R²)NC(O)—where R¹ and R² are H or some alkyl, aryl, cycloalkyl, perfluoroalkyl,or perfluoroaryl group. Examples include, but are not limited toN-ethylcarbamoyl, N,N-dimethylcarbamoyl, etc.

The term “amido” refers to the group of composition R¹CON(R²)— where R¹and R² are H or some alkyl, aryl, cycloalkyl, perfluoroalkyl, orperfluoroaryl group. Examples include, but are not limited to acetamido,N-ethylbenzamido, etc.

The term “acyl” refers to an organic acid group in which the OH of thecarboxyl group is replaced by some other substituent (RCO—). Examplesinclude, but are not limited to acetyl, benzoyl, etc.

In preferred embodiments, when a metal is designated by “M” or “M^(n)”,where n is an integer, it is recognized that the metal may be associatedwith a counterion.

The term “substituent” as used in the formulas herein, particularlydesignated by S or S^(n) where n is an integer, in a preferredembodiment refer to redox-active groups (subunits) that can be used toadjust the redox potential(s) of the subject compound. Preferredsubstituents include, but are not limited to, aryl, phenyl, cycloalkyl,alkyl, halogen, alkoxy, alkylthio, perfluoroalkyl, perfluoroaryl,pyridyl, cyano, thiocyanato, nitro, amino, alkylamino, acyl, sulfoxyl,sulfonyl, amido, and carbamoyl. In preferred embodiments, a substitutedaryl group is attached to a porphyrin or a porphyrinic macrocycle, andthe substituents on the aryl group are selected from the groupconsisting of aryl, phenyl, cycloalkyl, alkyl, halogen, alkoxy,alkylthio, perfluoroalkyl, perfluoroaryl, pyridyl, cyano, thiocyanato,nitro, amino, alkylamino, acyl, sulfoxyl, sulfonyl, amido, andcarbamoyl.

Particularly preferred substituents include, but are not limited to,4-chlorophenyl, 3-acetamidophenyl, 2,4-dichloro-4-trifluoromethyl).Preferred substituents provide a redox potential range of less thanabout 5 volts, preferably less than about 2 volts, more preferably lessthan about 1 volt.

The phrase “provide a redox potential range of less than about X volts”refers to the fact that when a substituent providing such a redoxpotential range is incorporated into a compound, the compound into whichit is incorporated has an oxidation potential less than or equal to Xvolts, where X is a numeric value.

The abbreviations “SHSU”, “SHMU” and “DHMU”, refer to “static-holesingle unit”, static-hole multi-unit” and dynamic hole multi-unit”,respectively.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a basic molecular memory unit “storage cell” of thisinvention. The basic memory device, a “storage cell” 100 comprises aworking electrode 101 electrically coupled to a storage medium 102comprising a multiplicity of storage molecules 105. The storage celloptionally includes an electrolyte 107 and a reference electrode 103.The storage medium has a multiplicity of different and distinguishableoxidation states, preferably a multiplicity of different anddistinguishable non-neutral oxidation states, and can change oxidation(charge) state when a voltage or signal is applied thereby adding orremoving one or more electrons.

FIG. 2 illustrates the disposition of the storage cell(s) of thisinvention on a chip.

FIG. 3 illustrates a preferred chip-based embodiment of this invention.A two-level chip is illustrated showing working electrodes 101,orthogonal reference electrodes 103, and storage elements 104.

FIG. 4. The three-dimensional architecture of a single memory storagecell (memory element) on the chip.

FIG. 5 illustrates the encoding of a prototypical DHMU storage moleculeusing hole-hopping states (the double-headed arrows indicate holehopping).

FIG. 6 illustrates porphyrin mono-thiols for attachment to a metal(e.g., gold) electrode.

FIG. 7 illustrates the modular synthesis of a SHMU storage molecule.

FIG. 8 illustrates a representative synthesis of a DHMU storagemolecule. Three porphyrin building blocks are prepared and metalatedwith magnesium or zinc. The synthetic strategy builds the two arms ofthe DHMU storage molecule separately, which are then coupled in thepenultimate step of the synthesis. Each arm is constructed via twoPd-mediated couplings, yielding the respective trimers. One trimer isiodinated at the ethyne, then joined with the other trimer in aheterocoupling process to form the H-like structure.

FIG. 9 illustrates writing to a molecular memory of this invention. Inpreferred embodiments, this is accomplished through the application ofvery short (e.g., microsecond) pulses applied at a voltage sufficient tooxidize a storage medium (e.g., a porphyrin) to the appropriate redoxstate as summarized in this figure. Thus, each redox state of thecomposite multiunit nanostructure (e.g. porphyrinic array) can beindependently accessed to provide one bit of resolution. This can beaccomplished via the electrochemical oxidation of the molecule instepwise increments.

FIG. 10 illustrates a frequency domain spectrum of the faradaic SVresponse. Note that the numerous harmonic frequency components depend onmany of the same voltammetric parameters (e.g., E^(o), E_(switch), scanrate, number of electrons, etc.) that govern the response observed incyclic voltammetry, and can be easily isolated in the frequency domain.

FIG. 11 illustrates a sinusoidal voltammetry system suitable for readoutof the memory devices of this invention.

FIG. 12 illustrates a computer system embodying the memory devicesdescribed herein. Typically the memory device will be fabricated as asealed “chip”. Ancillary circuitry on the chip and/or in the computerpermits writing bits into the memory and retrieving the writteninformation as desired.

FIG. 13 illustrates the memory devices of this invention integrated intoa standard computer architecture or computer system 200.

FIG. 14 illustrates synthesis scheme 1 for the synthesis of latentbenzaldehydes with various protecting groups for the p-thiol moiety.These are used in the synthesis of thiol-substituted porphyrins.

FIG. 15 illustrates synthesis scheme 2 for the synthesis ofbenzaldehydes with protected thiol groups. These are used in thesynthesis of thiol-derivatized porphyrins.

FIG. 16 illustrates synthesis scheme 3 for the synthesis of metallo-freeand zinc porphyrins each bearing three mesityl groups and one protectedp-thiophenyl group.

FIG. 17 illustrates synthesis scheme 4 for the synthesis of a zincporphyrin bearing three mesityl groups and one free thiol group.

FIG. 18 illustrates synthesis scheme 5 for the synthesis of a magnesiumporphyrin bearing three mesityl groups and one p-mercaptophenyl group.

FIG. 19 illustrates synthesis scheme 6 for the synthesis of metallo-freeand zinc porphyrins each bearing three groups to tune the oxidationpotential and one free or protected p-thiophenyl group.

FIG. 20 illustrates synthesis scheme 7 for the synthesis of metallo-freeand zinc porphyrins bearing four m-(thiocyanatomethyl)phenyl groups forhorizontal orientation on a gold surface.

FIG. 21 illustrates synthesis scheme 8 for the synthesis of metallo-freeand zinc porphyrins bearing two m-(thiocyanatomethyl)phenyl groups forhorizontal orientation on a gold surface.

FIG. 22 illustrates synthesis scheme 9 for the synthesis of metallo-freeand zinc porphyrins bearing four m-(S-acetylthiomethyl)phenyl groups forhorizontal orientation on a gold surface.

FIG. 23 illustrates the writing of bits on a porphyrin monolayer havingtwo non-neutral oxidation states. A plot of current versus time at 3applied voltages is illustrated. At 0-300 mV, no bit is set and the plotprovides a background signal. At 500-800 mV and at 800-1100 mV the firstand second bits are written, respectively.

FIG. 24 illustrates the read/write of a monomeric porphyrin. Current isplotted as a function of potential.

FIG. 25 illustrates background-subtracted faradaic read current.

FIG. 26 shows synthesis scheme 1 for the synthesis of Zn-2 from5-phenyldipyrromethane.

FIG. 27 shows synthesis scheme 2 for the synthesis of Zn-3 and Zn-4 fromZn-2.

FIG. 28 shows synthesis scheme 3 for the synthesis of Zn-8.

FIG. 29 shows equation 1 illustrating a first attempt to synthesize adipyrromethane by reacting commercially available4-methylthiobenzaldehyde with pyrrole to give the correspondingdipyrromethane (Gryko et al. (1999) J. Org. Chem. 64: 8634-8647).However, subsequent treatment with sodium tert-butoxide (Pinchart et al.(1999) Tetrahedron Lett. 40: 5479-5482), followed by quenching of theanion with acetyl chloride did not afford the desired product.

FIG. 30 shows Equation 2 illustrating the reaction of4-S-acetylthiobenzaldehyde (Gryko et al. (1999) J. Org. Chem. 64:8634-8647) with pyrrole to yield dipyrromethane 6.

FIG. 31 shows synthesis scheme 4 for the synthesis of Zn-9.

FIG. 32 shows synthesis scheme 5 for the synthesis of Zn-10.

FIG. 33 shows synthesis scheme 6 for the synthesis of Zn-13.

FIG. 34 illustrates a variety of linkers and their couling to aporphyrinic macrocycle.

FIG. 35 illustrates a synthesis of the aldehyde4-(S-acetylthio)-2,3,5,6-tetrafluorobenzaldehyde (9).

FIG. 36 illustrates substitution bromide with potassium thioacetate togive S-acetyl protected thiobenzaldehyde 10.

FIG. 37 illustrates a synthesis of aldehyde 11.

FIG. 38 illustrates a treatment of crude aldehyde 16 with potassiumthioacetate to yield aldehyde 17.

FIG. 39 illustrates a Pd-coupling of commercially availablepropiolaldehyde diethylacetal with 1-iodo-4-(S-acetylthio)benzene (1).

FIG. 40 illustrates scheme 1 for the synthesis of compound 3 using1-iodo-4-(S-acetylthio)benzene 1.

FIG. 41 illustrates scheme 2 for the synthesis of aldehyde 8.

FIG. 42 illustrates scheme 3 for the synthesis of aldehyde 15 startingfrom 4-bromobenzaldehyde.

FIG. 43 illustrates scheme 4 for the conversion of aldehydes 4, 8, 9,10, 11, 15 and 17 to the thiol-protected A₃B-porphyrins 19-25.

FIG. 44 illustrates scheme 5 for the conversion of acetal 18 to thedesired A₃B porphyrin.

FIG. 45 shows equation 1 illustrating the synthesis ofdiphenylethyne-linked ferrocene carboxaldehyde 30 via Pd-coupling ofethynylphenylferrocene 4 with 4-iodobenzaldehyde.

FIG. 46 shows equation 2 illustrating the treatment of4-ferrocenylbenzaldehyde 17 with excess pyrrole at room temperature toproduce 36.

FIG. 47 illustrates the reaction of ferrocenyldipyrromethane 36,4-(S-acetylthio)benzaldehyde 31 and 4-methylbenzaldehyde to provideprovided the expected porphyrins.

FIG. 48 illustrates scheme 1 for the synthesis of 4-iodophenylferrocene(1) in 30% yield.

FIG. 49 illustrates scheme 2 for the synthesis of4-{2-[4-(S-acetylthio)phenyl]ethynyl}phenylferrocene (5).

FIG. 50 illustrates scheme 3 for the synthesis of 11.

FIG. 51 shows scheme 4 for the synthesis of 12 using the Clemmensensystem (Zn/HgCl₂ amalgam and HCl).

FIG. 52 illustrates scheme 5 for the arylation of ferrocene using4-aminobenzyl alcohol to produce 4-ferrocenylbenzyl alcohol (16) and4-ferrocenylbenzaldehyde (17) which are then separatedchromatographically.

FIG. 53 illustrates scheme 6 for the synthesis of4-(bromomethyl)phenylferrocene (19).

FIG. 54 illustrates scheme 7 for the synthesis of a set ofS-acetylthio-derivatized alkylferrocenes with different length alkylchains.

FIG. 55 illustrates scheme 8 for the condensation of4-ferrocenylbenzaldehyde (17), 4-[S—(N-ethylcarbamoyl)thio]-benzaldehyde32 and 5-mesityldipyrromethane in the presence of BF₃-etherate and NH₄Clin acetonitrile followed by oxidation with DDQ to yield a crudeporphyrin mixture containing porphyrin 34.

DETAILED DESCRIPTION

This invention provides novel high density memory devices that areelectrically addressable permitting effective reading and writing, thatprovide a high memory density (e.g., 10¹⁵ bits/cm³), that provide a highdegree of fault tolerance, and that are amenable to efficient chemicalsynthesis and chip fabrication. The devices are intrinsically latchable,defect tolerant, and support destructive or non-destructive read cycles.

In a preferred embodiment, this invention provides an apparatus forstoring data (e.g., a “storage cell”). The storage cell includes a fixedelectrode electrically coupled to a “storage medium” having amultiplicity of different and distinguishable oxidation states wheredata is stored in the (preferably non-neutral) oxidation states by theaddition or withdrawal of one or more electrons from said storage mediumvia the electrically coupled electrode.

One embodiment of this invention is illustrated in FIG. 1. The basicmemory device, a “storage cell” 100 comprises a working electrode 101electrically coupled to a storage medium 102 comprising a multiplicityof storage molecules 105. The storage cell optionally includes anelectrolyte 107 and a reference electrode 103. The storage medium has amultiplicity of different and distinguishable oxidation states,preferably a multiplicity of different and distinguishable non-neutraloxidation states, and can change oxidation (charge) state when a voltageor signal is applied thereby adding or removing one or more electrons.Each oxidation state represents a particular bit. Where the storagemedium supports eight different and distinguishable oxidation states itstores one byte.

The storage medium remains in the set oxidation state until anothervoltage is applied to alter that oxidation state. The oxidation state ofthe storage medium can be readily determined using a wide variety ofelectronic (e.g. amperometric, coulometric, voltammetric) methodsthereby providing rapid readout.

The storage medium comprises molecules having a single oxidation stateand/or molecules having multiple different and distinguishablenon-neutral oxidation states. Thus, for example, in one embodiment, thestorage medium can comprise eight different species of storage moleculeseach having one non-neutral oxidation state and thereby store one byte.In another embodiment, the storage medium can comprise one species ofmolecule that has eight different and distinguishable oxidation statesand store one byte in that manner as well. As explained herein, a largenumber of different molecules having different numbers of oxidationstates can be used for the storage medium.

In certain preferred embodiments, the storage medium preferably utilizesmolecules employing weakly coupled arrays of porphyrins and/orporphyrinic macrocycles. The electrochemical potential in such moleculesis preferably tuned through the use of various substituents and centralmetals, but the molecules retain their distinctive oxidation potentialswhen they are incorporated into arrays. Accordingly this approachtypically involved the synthesis of a family of differently substitutedporphyrins (or other molecules) for incorporation into a moleculararray.

In other preferred embodiments, in order to simplify construction ofmolecular for information storage, this invention contemplates the useof polymeric molecules having multiple oxidation states where themonomeric subunits comprising the polymers are tightly coupled (e.g.directly linked as opposed to linking through a linker). The “tightcoupling” is manifested as a splitting in redox potentials of thestructurally identical subunits. Thus, for example, combination of twoidentical subunits each having two identical non-zero oxidation statescan result in dimer having four different and distinguishable non-zerooxidation states. This greatly simplifies fabrication of a storagemolecule as, in this instance, only a single type of subunit need besynthesized.

In any of the embodiments described herein, because molecular dimensionsare so small (on the order of angstroms) and individual molecules in thedevices of this invention can store multiple bits, the storage devicesof this invention therefore offer remarkably high storage densities(e.g. >10¹⁵ bits/cm³).

Moreover, the devices of this invention are capable of a degree ofself-assembly and hence easily fabricated. Because the devices areelectrically (rather than optically) addressed, and because the devicesutilize relatively simple and highly stable storage elements, they arereadily fabricated utilizing existing technologies and easilyincorporated into electronic devices. Thus, the molecular memory devicesof this invention have a number of highly desirable features:

Because the storage medium of the devices described herein iselectrically-addressed, the devices are amenable to the construction ofa multilayered chip architecture. An architecture compatible with such athree-dimensional structure is essential to achieve the objective of10¹⁵ bits/cm³. In addition, because writing and reading is accomplishedelectrically, many of the fundamental problems inherent with photonicsare avoided. Moreover, electrical reading and writing is compatible withexisting computer technology for memory storage.

In addition, the devices of this invention achieve a high level ofdefect tolerance. Defect tolerance is accomplished through the use ofclusters of molecules (up to several million in a memory cell). Thus,the failure of one or a few molecules will not alter the ability to reador write to a given memory cell that constitutes a particular bit ofmemory. In preferred embodiments, the basis for memory storage relies onthe oxidation state(s) of porphyrins or other porphyrinic macrocycles ofdefined energy levels. Porphyrins and porphyrinic macrocycles are wellknown to form stable radical cations. Indeed, the oxidation andreduction of porphyrins provide the foundation for the biologicalprocesses of photosynthesis and respiration. Porphyrin radical cationscan be formed chemically on the benchtop exposed to air. We know of noother class of molecules with such robust electroactive properties.

Preferred storage molecules of this invention molecule (e.g., SHMU orDHMU) can hold multiple holes, corresponding to multiple bits. Incontrast, the dyes (photochromic, electrochromic, redox) and molecularmachines are invariably bistable elements. Bistable elements existeither in a high/low state and hence can only store a single bit. TheSHMU and DHMU are unique molecular nanostructures providing resilientstorage of multiple bits.

Reading can be accomplished non-destructively or destructively asrequired in different chip applications. The speed of reading isconservatively estimated to lie in the MHz to GHz regime. Memory storageis inherently latchable due to the stability of the porphyrin or otherporphyrinic macrocycle radical cations. Oxidation of the porphyrins orother porphyrinic macrocycles can be achieved at relatively lowpotential (and at predesignated potentials through synthetic design),enabling memory storage to be achieved at very low power. Porphyrins andporphyrin radical cations are stable across a broad range oftemperatures, enabling chip applications at low temperature, roomtemperature, or at elevated temperatures.

Fabrication of the devices of this invention relies on known technology.The synthesis of the storage media takes advantage of establishedbuilding block approaches in porphyrin and other porphyrinic macrocyclechemistry. Synthetic routes have been developed to make the porphyrinand porphyrinic macrocycle building blocks, to join them in covalentnanostructures, and to purify them to a high level (>99%).

In preferred embodiments, the storage medium nanostructures are designedfor directed self-assembly on gold surfaces. Such self-assemblyprocesses are robust, result in the culling out of defective molecules,and yield long-range order in the surface-assembled cluster.

Porphyrin-thiols have been assembled on electroactive surfaces. Thearrays that define the addressable bits of memory can be achievedthrough conventional microfabrication techniques. The storage moleculesare self-assembled onto these electrode arrays and attached to the goldsurface using conventional dipping methods.

I. Uses of the Storage Device.

One of ordinary skill in the art will appreciate that the memory devicesof this invention have wide applicability in specialized andgeneral-purpose computer systems. Of course commercial realization ofthe device(s) will be facilitated by the adoption of computerarchitecture standards compatible with this technology. In addition,commercial adoption of this technology will be facilitated by the use ofother molecular electronic components that will serve as on-chip buffersand decoders (that is, molecular logic gates), and the like. Inaddition, commercialization will be facilitated by the development of afull manufacturing infrastructure.

Regardless, prior to the development of a fully integrated design andmanufacturing platform for molecular electronic information storage andtransfer, even early generation prototype molecular memory devicesdescribed herein have utility in highly specialized military and/orstealthy applications. For example, a prototype 1024/512-bit molecularmemory device has sufficient capacity to hold a substantial base ofpersonal and/or other proprietary information. This information could betransported anywhere in the world virtually undetected owing to theextremely small size of the device. If detected, the memory device iseasily erased simply by applying a low potential reverse bias currentacross all memory cells. This protection mechanism can be readilyincorporated into any type of transport architecture designed for thememory device.

The memory devices of this invention have sufficient capacity to holdpersonal information (e.g. medical, personal identification, financialinformation on a “smart card”). Even a memory device that degrades uponmultiple read cycles is extremely useful if the number of read cycles ishighly limited (perhaps only one). A memory device that degrades uponmultiple read cycles or simply with time is also useful in applicationswhere long-term data persistence is not needed or is strategicallyunwise. Thus, numerous strategically important applications for earlygeneration memory devices present themselves. Successes of the memorydevices in these applications will foster even more rapid full-scalecommercialization of the technology.

II. Architecture of the Storage Device.

The basic storage cell (electrode(s) and storage medium) of thisinvention can be incorporated into a functional device in a wide varietyof configurations. One preferred embodiment of this invention isillustrated in FIGS. 1 and 2. The basic memory device, a “storage cell”100 comprises one or more working electrodes 101 electrically coupled toa storage medium 102 comprising a multiplicity of storage molecules 105.The storage cell optionally includes an electrolyte 107 and one or morereference electrode(s) 103. The storage medium has a multiplicity ofdifferent and distinguishable oxidation states, preferably amultiplicity of different and distinguishable non-neutral oxidationstates, and can change oxidation (charge) state when a voltage or signalis applied thereby adding or removing one or more electrons. Eachoxidation state represents a particular bit, however, in certainembodiments, where the oxidation states are not fully independentlyaddressable, it may take as many as eight oxidation states toindependently write three bits.

The storage medium generally remains in the set oxidation state untilanother voltage is applied to alter that oxidation state. The oxidationstate of the storage medium can be readily determined using a widevariety of electronic (e.g. amperometric, coulometric, voltammetric)methods thereby providing rapid readout.

The storage medium comprises molecules having a single oxidation stateand/or molecules having multiple different and distinguishablenon-neutral oxidation states. Thus, for example, in one embodiment, thestorage medium can comprise eight different species of storage moleculeseach having one non-neutral oxidation state and thereby store one byte.In another embodiment, the storage medium can comprise one species ofmolecule that has eight different and distinguishable oxidation statesand store one byte in that manner as well. As explained herein, a largenumber of different molecules having different numbers of oxidationstates can be used for the storage medium.

Because molecular dimensions are so small (on the order of angstroms)and individual molecules in the devices of this invention can storemultiple bits, the storage devices of this invention therefore offerremarkably high storage densities (e.g. >10¹⁵ bits/cm³).

One chip-based embodiment of this invention is illustrated in FIG. 2. Asillustrated in FIG. 2 the storage medium 102 is disposed in a number ofstorage locations 104. Each storage location is addressed by a workingelectrode 101 and a reference electrode 103 so that the storage medium102 combined with the electrodes forms a storage cell 100 at eachstorage location.

One particularly preferred chip-based embodiment is illustrated in FIG.3. In the illustrated embodiment, a plurality of working electrodes 101and reference electrodes 103 are illustrated each addressing storagemedia 102 localized at discrete storage locations thereby forming aplurality of storage cells 100. Multiple storage cells can be associatedwith a single addressing electrode as long as oxidation states of thestorage cells are distinguishable from each other. It should be notedthat this forms a functional definition of a storage cell. Where twodiscrete areas of storage medium are addressed by the same electrode(s)if the storage media comprise the same species of storage molecule thetwo discrete areas will functionally perform as a single storage cell,i.e. the oxidation states of both locations will be commonly set, and/orread, and/or reset. The added storage location, however, will increasethe fault tolerance of the storage cell as the functional storage cellwill contain more storage molecules. In another embodiment, eachindividual storage cell is associated with a single addressingelectrode.

In preferred embodiments, the storage medium comprising the storagecells of a memory device are all electrically coupled to one or morereference electrodes. The reference electrode(s) can be provided asdiscrete electrodes or as a common backplane.

The chip illustrated in FIG. 3 has two levels of working electrodes andhence two levels of storage cells 100 (with numerous storage cells oneach level). Of course, the chip can be fabricated with a single levelof electrodes and memory element or literally hundreds or thousands ofdifferent levels of storage cell(s), the thickness of the chip beinglimited essentially by practical packaging and reliability constraints.

In certain preferred embodiments the storage medium is juxtaposed to adielectric medium to insure electrical connectivity to a referencevoltage (e.g. a reference electrode, a reference backplane, etc.). Inparticularly preferred embodiments, a layer of dielectric materialimbedded with counterions to ensure electrical connectivity to thereference electrode and stability of the cationic species in the absenceof applied potential (latching), is disposed between the referenceworking electrode(s).

Dielectric materials suitable for the devices of this invention are wellknown to those of skill in the art. Such materials include, but are notlimited to Nafion™, cellulose acetate, polystyrene sulfonate,poly(vinylpyridine), electronically conducting polymers such aspolypyrrole and polyaniline, etc.

While, in some preferred embodiments, feature sizes are rather large(e.g. memory elements approximately (10×10×10 μm) and electrodethickness ˜200 nm, feature size can be reduced at will so that featuresizes are comparable to those in conventional silicon-based devices(e.g., 50 nm-100 nm on each axis).

In one particularly preferred embodiment, the storage device includes:(1) A metal (e.g. gold) working electrode (e.g., 200 nm thick),deposited on a nonconducting base, and line-etched to achieve electrodewidths of 10's to 100's of nm. (2) A monolayer of self-assembledporphyrinic nanostructures (storage molecules 105) attached to the goldsurface via the sulfur atom of the thiophenol group. (3) A 100-nm thicklayer of dielectric material 107 embedded with counterions to ensureelectrical connectivity to the reference electrode and stability of thecationic species in the absence of applied potential (latching). (4) A200-nm thick nonpolarizable reference electrode 103 line etched in thesame fashion as those of the working electrode 101, but assembled withlines orthogonal to the latter electrode. (5) A mirror image constructthat utilizes the same reference electrode. Thus, in one embodiment, thethree-dimensional architecture of a single memory storage location(memory element) on the chip will look as indicated in FIG. 4.

While the discussion herein of electrodes is with respect to goldelectrodes, it will be recognized that numerous other materials will besuitable. Thus, electrode materials include, but are not limited togold, silver, copper, other metals, metal alloys, organic conductors(e.g. doped polyacetylene, doped polythiophene, etc.), nanostructures,crystals, etc.

Similarly, the substrates used in the fabrication of devices of thisinvention include, but are not limited to glasses, silicon, minerals(e.g. quartz), plastics, ceramics, membranes, gels, aerogels, and thelike.

III. Fabrication and Characterization of the Storage Device.

A) Fabrication.

The memory devices of this invention can be fabricated using standardmethods well known to those of skill in the art. In a preferredembodiment, the electrode layer(s) are applied to a suitable substrate(e.g. silica, glass, plastic, ceramic, etc.) according to standard wellknown methods (see, e.g., Choudhury (1997) The Handbook ofMicrolithography, Micromachining, and Microfabrication, Soc.Photo-Optical Instru. Engineer, Bard & Faulkner (1997) Fundamentals ofMicrofabrication). In addition, examples of the use of micromachiningtechniques on silicon or borosilicate glass chips can be found in U.S.Pat. Nos. 5,194,133, 5,132,012, 4,908,112, and 4,891,120.

In one preferred embodiment a metal layer is beam sputtered onto thesubstrate (e.g., a 10 nm thick chromium adhesion layer is sputtered downfollowed by a 200 nm thick layer of gold). Then maskless laser ablationlithography (see below), performed e.g., with a Nd:YAG laser, is used tocreate features with micron dimensions, or with an excimer laser tocreate features of nanometer dimensions) will create an array ofparallel lines of conductor (e.g., gold), used as the working electrodeswith dimensions ranging between a few microns to a tens of nanometers.

Once the electrode array is formed, the entire array, or portions of thearray, or individual electrodes are wetted (e.g. immersed or spotted)with one or more solutions of the appropriate derivatized storage media(e.g. thiol-substituted porphyrin nanostructures), and the constituentsof the memory medium (e.g., monomeric porphyrin subunits) self-assembleon the micro-sized gold arrays to form the memory elements. It will beappreciated that different solutions can be applied to different regionsof the electrode array to produce storage cells comprising differentstorage medium. Methods of spotting different reagents on surfaces (e.g.on glass surfaces) at densities up to tens of thousands of differentspecies/spots per cm² are known (see, e.g., U.S. Pat. No. 5,807,522).

Then a suitable electrolyte layer (e.g. a thin layer of Nafion polymer)approximately 1 nm to 1000 nm, preferably about 100 nm to about 500 nm,more preferably about 10 nm to about 100 nm and most preferably aboutone hundred nanometers thick) will be cast over the entire surface ofthe chip. This polymer serves to hold the electrolyte forelectrochemical reaction. Finally, the entire chip is coated with alayer (e.g., 10 nm to about 1000 nm, more preferably 100 nm to about 300nm and most preferably about 200 nm of conducting material (e.g. silver)which acts as a reference electrode 103.

The chip is then turned 90 degrees, and maskless laser ablationlithography will be performed again to create a second array of parallellines that are perpendicular to the original set. This forms a threedimensional array of individual memory elements, where each element isformed by the intersection of these two perpendicular linear arrays (seeFIG. 4).

Each individual element can be addressed by selecting the appropriate Xand Y logic elements, corresponding to one gold working electrode andone reference electrode separated by the Nafion polymer/electrolytelayer. Since this structure is inherently three dimensional, it shouldbe possible to extend the array into the Z-direction, creating a 3-Darray of memory elements as large as it is feasible to connect to.

These structures are initially created on the micron scale. It ispossible to decrease the size of these structures to sub-microndimensions. It is possible to create these structures on a scale similarto silicon microstructures created with conventional nanolithographictechniques (i.e. 100-200 nm). This would allow the interfacing of thememory elements with conventional silicon-based semiconductorelectronics.

In the laser-ablation lithography discussed above, coherent light issent through a beam splitter (50% transmittance) and reflected by amirror to make two nearly parallel identical beams (Rosenwald et al.(1998) Anal. Chem., 70: 1133-1140). These beams are sent through e.g., a50 cm focal length lens for ease in focusing to a common point. Theplacement of the beams is fine-tuned to allow complete overlap of themode structure of the laser spot. Higher order interference patterns areminimized through the use of high quality optics (1/10 wave surfaceflatness). This ensures that the variation between intensity maxima andminima in the first order will be several orders of magnitude largerthan those formed with second and higher orders. This produces awell-defined pattern of lines across the electrode surface, where thespacing between points of positive interference (D) can be approximatedby the Bragg Equation: nλ=2D sin(θ/2), where λ=wavelength, θ=anglebetween the beams, and n is order. For example, when a Nd:YAG is used at1064 nm, the recombination of the two beams in this manner generates aninterference pattern with ˜2 micron spacing when the angle between the 2beams is 15°. The interference pattern spacing can easily be changed bymodifying the angle between the beams. Attenuation of the beam wasaccomplished by inserting one or more neutral density filters before thebeam splitter. In this way, the exposure of the gold layer to the Nd-YAGinterference pattern can be performed at different beam attenuations toproduce power densities between 1 and 100 MW/cm².

B) Electrically Coupling Storage Medium to Electrode.

In the storage devices of this invention, the storage medium iselectrically coupled to one or more electrodes. The term “electricalcoupling” is used to refer to coupling schemes that permit the storagemedium to gain or lose electrons to the electrode. The coupling can be adirect attachment of the storage medium to the electrode, or an indirectattachment (e.g. via a linker). The attachment can be a covalentlinkage, an ionic linkage, a linkage driven by hydrogen bonding or caninvolve no actual chemical attachment, but simply a juxtaposition of theelectrode to the storage medium. In some embodiments, the electrode canbe some distance (e.g., about 5 Å to about 50 Å) from the storage mediumand electrical coupling can be via electron tunneling.

In some preferred embodiments, a “linker” is used to attach themolecule(s) of the storage medium to the electrode. The linker can beelectrically conductive or it can be sufficient position the molecule(s)of the storage medium such that electrons can pass directly orindirectly between the electrode and a molecule of the storage medium.

The manner of linking a wide variety of compounds to various surfaces iswell known and is amply illustrated in the literature. Means of couplingthe molecules comprising the storage medium will be recognized by thoseof skill in the art. The linkage of the storage medium to a surface canbe covalent, or by ionic or other non-covalent interactions. The surfaceand/or the molecule(s) may be specifically derivatized to provideconvenient linking groups (e.g. sulfur, hydroxyl, amino, etc.).

The linker can be provided as a component of the storage mediummolecule(s) or separately. Linkers, when not joined to the molecules tobe linked are often either hetero- or homo-bifunctional molecules thatcontain two or more reactive sites that may each form a covalent bondwith the respective binding partner (i.e. surface or storage mediummolecule). When provided as a component of a storage molecule, orattached to a substrate surface, the linkers are preferably spacershaving one or more reactive sites suitable for bonding to the respectivesurface or molecule.

Linkers suitable for joining molecules are well known to those of skillin the art and include, but are not limited to any of a variety of, astraight or branched chain carbon linker, or a heterocyclic carbonlinker, amino acid or peptide linkers, and the like. Particularlypreferred linkers include, but are not limited to 4,4′-diphenylethyne,4,4′-diphenylbutadiyne, 4,4′-biphenyl, 1,4-phenylene, 4,4′-stilbene,1,4-bicyclooctane, 4,4′-azobenzene, 4,4′-benzylideneaniline, and4,4″-terphenyl. Linkers include molecules that join one or moremolecules of the storage medium to the electrode(s).

A variety of suitable linkers are illustrated in FIG. 34, although incertain embodiments, this invention excludes linker A in FIG. 34. Thesynthesis of these linkers is described in detail in Example 4. Usingthe teaching provided herein, a wide variety of other suitable linkerscan routinely be produced by one of ordinary skill in the art.

C) Addressing the Memory Cells.

Addressing of the storage cell(s) in the devices of this invention isrelatively straightforward. In a simple approach a discrete pair ofelectrodes (one working and one reference electrode) can be connected toevery storage cell. Individual reference electrodes, however are notrequired and can be replaced with one or more common referenceelectrodes connected to all or to a subset of all of the storageelements in a particular device. Alternatively, the common referenceelectrodes can be replaced with one or more conductive “backplanes” eachcommunicating to all, or to a subset, of the storage cells in aparticular device.

Where the storage cells contain identical storage media, each storagecell is preferably addressed with a separate working electrode so thatthe storage (oxidation) states of the storage cells can be distinguishedfrom each other. Where the storage cells contain different storage mediasuch that the oxidation states of one storage cell is different anddistinguishable from the oxidation states of another storage cell, thestorage cells are preferably addressed by a common working electrodethereby reducing the number of electrodes in a device.

In one preferred embodiment, the storage devices of this inventioncontain 64, 128, 256, 512, 1024 or more storage locations per layer (64,128, 256, 512, 1024 or more locations in the mirror image architecture)with each location capable of holding a multiple-bit SHMU or DHMU word.Accordingly, a preferred 1024-bit SHMU or a preferred 512-bit DHMU chipwill contain 8 wiring interconnects on each of the three electrode gridsin the 3-dimensional WPDRDPW architecture illustrated in FIG. 4.

D) Characterization of the Memory Device.

The performance (e.g. operating characteristics) of the memory devicesof this invention is characterized by any of a wide variety of methods,most preferably by electrochemical methods (amperometry, sinusoidalvoltammetry and impedance spectroscopy, see, e.g., Howell et al. (1986)Electroanal. Chem., 209: 77-90; Singhal et al. (1997) Anal. Chem., 69:1662-1668; Schick et al. (1989) Am. Chem. Soc. 111: 1344-1350), atomicforce microscopy, electron microscopy and imaging spectroscopic methods.Surface-enhanced resonance and Raman spectroscopy are also used toexamine the storage medium on the electrodes.

Among other parameters, characterization of the memory devices (e.g.,memory cells) involves determining the number of storage mediummolecules (e.g., porphyrin arrays) required for defect-tolerantoperation. Defect tolerance includes factors such as reliably depositingthe required number of holes to write the desired digit and accuratelydetecting the numbers/hopping rates of the holes.

The long-term resistance of electron holes to charge-recombination inthe solid-phase medium of the device package is also determined. Usingthese parameters, the device architecture can be optimized forcommercial fabrication.

IV. Architecture of the Storage Medium.

The storage medium used in the devices of this invention comprises oneor more species of storage molecule. A preferred storage medium ischaracterized by having a multiplicity of oxidation states. Thoseoxidation states are provided by one or more redox-active units. Aredox-active unit refers to a molecule or to a subunit of a moleculethat has one or more discrete oxidation states that can be set byapplication of an appropriate voltage. Thus, for example, in oneembodiment, the storage medium can comprise one species of redox-activemolecule where that molecule has two or more (e.g. 8) different anddistinguishable oxidation states. Typically, but not necessarily, suchmulti-state molecules will be composed of several redox-active units(e.g. porphyrins or ferrocenes). In another exemplary embodiment, thestorage medium can comprise two or more different species of storagemolecule. Each storage molecule comprises at least one redox-activeunit, but can easily contain two or more redox-active units. Where eachspecies of storage molecule has a single, non-neutral, oxidation state,the storage medium achieves multiple bit storage by having a pluralityof such molecules where each molecule has a different anddistinguishable oxidation state (e.g. each species of molecule oxidizesat a different and distinguishable potential). Of course, each speciesof molecule can have a multiplicity of different and distinguishableoxidation states. Thus, a storage medium comprising eight differentspecies of storage molecule where each of the eight species has eightdifferent and distinguishable oxidation states, will be able to store 64(8×8) bits of information.

As indicated above, the storage medium can be broken down intoindividual, e.g., spatially segregated, storage locations. Each storageelement can have a storage medium that is the same or different from theother storage elements in the chip and/or system. Where the storageelements are of identical composition, in preferred embodiments, theyare separately addressed so that information in one element can bedistinguished from information in another element. Where the storageelements are of different composition they can be commonly addressed(where the oxidation states of the commonly addressed storage elementsare distinguishable) or they can be individually addressed.

In certain preferred embodiments the storage medium is juxtaposed to adielectric medium to insure electrical connectivity to a referencevoltage (e.g. a reference electrode, a reference backplane, etc.). Inparticularly preferred embodiments, a layer of dielectric material isimbedded with counterions to ensure electrical connectivity to thereference electrode and stability of the cationic species in the absenceof applied potential (latching) is disposed between the referenceworking electrode(s).

Dielectric materials suitable for the devices of this invention are wellknown to those of skill in the art. Such materials include, but are notlimited to nafion, cellulose acetate, polystyrene sulfonate,poly(vinylpyridine), electronically conducting polymers such aspolypyrrolic acid and polyaniline, etc.

The porphyrinic macrocycles identified herein are ideally suited formolecular based memory storage. The porphyrinic macrocycles, andespecially the porphyrins, have unique electroactive properties, awell-developed modular synthetic chemistry, and in conjunction withthiols, and other linkers described herein, undergo directedself-assembly on electroactive surfaces.

In addition, as described below, the porphyrinic macrocycles are wellsuited for the design of multi-bit storage systems. In preferredembodiments, this invention contemplates three fundamental architecturesfor the storage medium; static hole single-unit (SHSU) storage (e.g.SHSU molecules), static hole multi-unit (SHMU) storage (e.g. SHSUmolecules), and dynamic hole multi-unit (DHMU) storage (e.g. DHMUmolecules).

A) Static Hole Single Unit (SHSU) Storage.

In the simplest embodiments of this invention, the storage mediumcomprises one or more molecules wherein each molecule has onenon-neutral oxidation state. Thus, each molecule is capable of storingone bit (e.g. bit=1 when oxidized and bit=0 when neutral). A number ofdifferent species of static hole single unit storage molecules can beassembled into a single storage medium. Thus, for example a number ofdifferent ferrocenes, or a number of different porphyrins, orcombinations of porphyrin and ferrocene monomers can be combined into asingle storage medium.

In one preferred embodiment, a molecule comprising a static hole singleunit molecular memory has the formula shown in Formula I.

where L is a linker, M is a metal (e.g., Fe, Ru, Os, Co, Ni, Ti, Nb, Mn,Re, V, Cr, W), S¹ and S² are substituents independently selected fromthe group consisting of aryl, phenyl, cycloalkyl, alkyl, halogen,alkoxy, alkylthio, perfluoroalkyl, perfluoroaryl, pyridyl, cyano,thiocyanato, nitro, amino, alkylamino, acyl, sulfoxyl, sulfonyl, imido,amido, and carbamoyl. In preferred embodiments, a substituted aryl groupis attached to the porphyrin, and the substituents on the aryl group areselected from the group consisting of aryl, phenyl, cycloalkyl, alkyl,halogen, alkoxy, alkylthio, perfluoroalkyl, perfluoroaryl, pyridyl,cyano, thiocyanato, nitro, amino, alkylamino, acyl, sulfoxyl, sulfonyl,imido, amido, and carbamoyl.

Particularly preferred substituents include, but are not limited to,4-chlorophenyl, 3-acetamidophenyl, 2,4-dichloro-4-trifluoromethyl).Preferred substituents provide a redox potential range of less thanabout 2 volts. X is selected from the group consisting of a substrate, areactive site that can covalently couple to a substrate, and a reactivesite that can ionically couple to a substrate. It will be appreciatedthat in some embodiments, L-X can be replaced with another substituent(S³) like S¹ or S². In certain embodiments, L-X can be present orabsent, and when present preferably is4-(2-(4-mercaptophenyl)ethynyl)phenyl, 4-mercaptomethylphenyl,4-hydroselenophenyl, 4-(2-(4-hydroselenophenyl)ethynyl)phenyl,4-hydrotellurophenyl, or 4-(2-(4-hydrotellurophenyl)ethynyl)phenyl.

The oxidation state of molecules of Formula I is determined by the metaland the substituents. Thus, particular preferred embodiments areillustrated by Formulas II-VII, (listed sequentially) below:

The ferrocenes listed above in Formulas II through VII provide aconvenient series of one-bit molecules having different anddistinguishable oxidation states. Thus the molecules of Formulas IIthrough VII have oxidation states (E_(1/2)) of +0.55 V, +0.48V, +0.39 V,+0.17 V, −0.05 V, and −0.18 V, respectively, and provide a convenientseries of molecules for incorporation into a storage medium of thisinvention. It will be appreciated that the oxidation states of themembers of the series can be routinely altered by changing the metal (M)or the substituents.

B) Static Hole Multi-Unit (SHSU) Storage.

Static hole multi-unit (SHSU) molecular memories typically comprise amultiplicity of redox-active subunits. In a preferred embodiment, theredox-active subunits are covalently linked to form a single moleculeand are selected to have different and distinguishable oxidation states,preferably a multiplicity of different and distinguishable non-neutraloxidation states. Thus, in this configuration a single molecule can havemultiple (e.g. 2, 4, 8, 16, 32, 64, 128, 512 etc.) different non-neutraloxidation states.

In one particularly preferred embodiment the static hole multi-unitmolecular memory is a “static hole multiporphyrin molecular memory”(SHMMM) storage system. In this embodiment, the redox-active subunitsare porphyrinic macrocycles, most preferably porphyrins. The porphyrinscan be arranged in a wide variety of configurations (e.g. linearpolymers, branched polymers, arrays, etc.), however, linearconfigurations are well suited to the practice of this invention.

One particularly preferred linear configuration is illustrated byFormula VIII.

where S¹, S², S³, and S⁴ are substituents independently selected fromthe group consisting of aryl, phenyl, cycloalkyl, alkyl, halogen,alkoxy, alkylthio, perfluoroalkyl, perfluoroaryl, pyridyl, cyano,thiocyanato, nitro, amino, alkylamino, acyl, sulfoxyl, sulfonyl, imido,amido, and carbamoyl wherein said substituents provide a redox potentialrange of less than about 2 volts, M¹, M², M³, and M⁴ are independentlyselected metals (e.g., Zn, Mg, Cd, Hg, Cu, Ag, Au, Ni, Pd, Pt, Co, Rh,Ir, Mn, B, Al, Ga, Pb, and Sn), K¹, K², K³, K⁴, K⁵, K⁶, K⁷, K⁸, K⁹, K¹⁰,K¹¹, K¹², K¹³, K¹⁴, K¹⁵, and K¹⁶ are independently selected from thegroup consisting of N, O, S, Se, Te, and CH, J¹, J², and J³ areindependently selected linkers, L¹, L², L³, and L⁴ are present or absentand, when present are independently selected linkers, X¹, X², X³, and X⁴are independently selected from the group consisting of a substrate, areactive site that can covalently couple to a substrate, and a reactivesite that can ionically couple to a substrate, and E¹ and E² areterminating substituents independently aryl, phenyl, cycloalkyl, alkyl,halogen, alkoxy, alkylthio, perfluoroalkyl, perfluoroaryl, pyridyl,cyano, thiocyanato, nitro, amino, alkylamino, acyl, sulfoxyl, sulfonyl,imido, amido, or carbamoyl wherein said substituents provide a redoxpotential range of less than about 2 volts. In preferred embodiments,the molecule has at least two, preferably at least 4, more preferably atleast 8, and most preferably at least 16, at least 32, at least 64 or atleast 128 different and distinguishable oxidation states. In someembodiments, one or more of the linker/reactive site subunits (L¹-X¹,L²-X², L³-X³, or L⁴-X⁴), can be eliminated and replaced with asubstituent independently selected from the same group as S¹, S², S³, orS⁴.

In preferred embodiments, the substituents are selected so that themolecule illustrated by Formula XVIII has at least 2, more preferably atleast 4 and most preferably at least 8 different and distinguishableoxidation states.

In certain preferred embodiments, J¹l, J², and J³ are independently4,4′-diphenylethyne, 4,4′-diphenylbutadiyne, 4,4′-biphenyl,1-4-phenylene, 4,4′-stilbene, 1,4-bicyclooctane, 4,4′-azobenzene,4,4′-benzylideneaniline, or 4,4″-terphenyl.

L¹-X¹, L²-X², L³-X³, and L⁴-X⁴ are independently present or absent and,when present, can include 4-(2-(4-mercaptophenyl)ethynyl)phenyl,4-mercaptomethylphenyl, 4-hydroselenophenyl,4-(2-(4-hydroselenophenyl)ethynyl)phenyl, 4-hydrotellurophenyl, and4-(2-(4-hydrotellurophenyl)ethynyl)phenyl.

In a particularly preferred embodiment, K¹, K², K³, K⁴, K⁵, K⁶, K⁷, K⁸,K⁹, K¹⁰, K¹¹, K¹², K¹³, K¹⁴, K¹⁵, and K¹⁶ are the same, M¹ and M³ arethe same, M² and M⁴ are the same and different from M¹ and M³, S¹ and S²are the same; and S³ and S⁴ are the same and different from S¹ and S².

In a most preferred embodiment, the metals (M¹, M², M³, and M⁴) and thesubstituents (S¹, S², S³, and S⁴) are selected so that each porphyrinhas two non-neutral oxidation states. L¹-X¹, L²-X², L³-X³, and L⁴-X⁴provide convenient linkers for attaching the molecule to a substrate(e.g. an electrode). With each subunit having two oxidation states, thesubunits can be configured so that the entire molecule has 8 differentand distinguishable oxidation states. One such molecule is illustratedby Formula IX.

The porphyrin metalation state alters between Mg and Zn in proceedingfrom one end to the other. The different metalation state alters theredox characteristics of the porphyrins. In particular, magnesiumporphyrins are more easily oxidized than zinc porphyrins.Differentiation of the oxidation potentials of the left-most pair of Znand Mg porphyrins from those of the right-most pair is achieved throughthe use of different substituents (Ar², right pair; Ar¹, left pair)attached to the meso- (and/or to the β-) positions. The porphyrins arejoined via linkers (e.g. p,p′-diarylethyne linkers). These constrain theporphyrins at fixed distances from each other. In addition, eachporphyrin bears a linker (e.g., a thiol) for attachment to anelectroactive surface such as gold.

Information is stored in the SHMU storage molecule by removing electronsfrom the porphyrin constituents (leaving a hole and forming a π-cationradical (Strachan et al. (1997) J. Am. Chem. Soc., 119: 11191-11201; Liet al. (1997) J. Mater. Chem. 7: 1245-1262, and Seth et al. (1996) J.Am. Chem. Soc. 118: 11194-11207; Seth et al. (1994) J. Am. Chem. Soc.116: 10578-10592). The redox characteristics of the Zn and Mg porphyrinsin conjunction with the substituents Ar¹ and Ar² permit oxidation toform in sequence, (MgAr¹⁽⁺⁾, others neutral), (MgAr¹⁽⁺⁾, ZnAr¹⁽⁺⁾, withMgAr² and ZnAr² neutral], and so forth until two holes have been removedfrom all of the four metalloporphyrins, i.e., [MgAr¹⁽⁺⁺⁾, ZnAr¹⁽⁺⁺⁾,MgAr²⁽⁺⁺⁾, ZnAr²⁽⁺⁺⁾]. Thus, up to eight holes can be stored in thememory with each unique oxidation state serving as a digit of a basiceight-bit memory element. This is illustrated below in Table 1.

TABLE 1 Bit architecture in a prototype SHMU storage molecule. SubunitP1 Subunit P2 Subunit P3 Subunit P4 Memory MgAr¹ ZnAr¹ MgAr² ZnAr²“parity” 0 0 0 0 0 0 0 + 0 0 0 0 0 1 + + 0 0 0 1 0 ++ + 0 0 0 1 1 ++ ++0 0 1 0 0 ++ ++ + 0 1 0 1 ++ ++ + + 1 1 0 ++ ++ ++ + 1 1 1 ++ ++ ++ ++

The synthetic methodologies already established permit the extension ofthe linear architecture, thus increasing the dynamic range of the basicmemory element well beyond the three bits indicated. Conversely, themolecule could be reduced to two subunits thereby encoding 2 bits (+“parity”). In addition, subunits can be engineered that have more thantwo oxidation states. Thus for example, molecules and/or subunits can beengineered that have virtually any number (e.g., 2, 4, 8, 16, 32, 64,128, etc.) of different and distinguishable oxidation states.

In other embodiments, single molecule, non-polymeric molecules canmaintain multiple oxidation states and thereby support multiple bits. Inpreferred embodiments, such molecules comprise multiple redox-activesubunits. Certain preferred molecules have 2, 3, 5, 8, or even moredifferent and distinguishable non-neutral oxidation states. One suchmolecule is illustrated by Formula XI.

where, F is a redox-active subunit (e.g., a ferrocene, a substitutedferrocene, a metalloporphyrin, or a metallochlorin, etc.), J¹ is alinker, M is a metal (e.g., Zn, Mg, Cd, Hg, Cu, Ag, Au, Ni, Pd, Pt, Co,Rh, Ir, Mn, B, Al, Ga, Pb, and Sn), S¹ and S² are independently selectedfrom the group consisting of aryl, phenyl, cycloalkyl, alkyl, halogen,alkoxy, alkylthio, perfluoroalkyl, perfluoroaryl, pyridyl, cyano,thiocyanato, nitro, amino, alkylamino, acyl, sulfoxyl, sulfonyl, imido,amido, and carbamoyl wherein said substituents provide a redox potentialrange of less than about 2 volts, K¹, K², K³, and K⁴ are independentlyselected from the group consisting of N, O, S, Se, Te, and CH; L is alinker; X is selected from the group consisting of a substrate, areactive site that can covalently couple to a substrate, and a reactivesite that can ionically couple to a substrate. In some embodiments L-Xcan be eliminated and replaced with a substituent independently selectedfrom the same group as S¹ or S².

In preferred embodiments, the molecule has at least three different anddistinguishable oxidation states. Particularly preferred variants ofthis storage molecule are illustrated by Formulas XII, XIII, and XIV,below:

where K⁵, K⁶, K⁷, and K⁸ are independently selected from the groupconsisting of N, O, S, Se, Te, and CH; S² and S³ are independentlyselected from the group consisting of aryl, phenyl, cycloalkyl, alkyl,halogen, alkoxy, alkylthio, perfluoroalkyl, perfluoroaryl, pyridyl,cyano, thiocyanato, nitro, amino, alkylamino, acyl, sulfoxyl, sulfonyl,imido, amido, and carbamoyl wherein said substituents provide a redoxpotential range of less than about 2 volts, and M² is a metal (e.g., Zn,Mg, Cd, Hg, Cu, Ag, Au, Ni, Pd, Pt, Co, Rh, Ir, Mn, B, Al, Ga, Pb, andSn). These molecules can exist in three different and distinguishableoxidation states. The values of the oxidation states are determined bythe metal (M), the substituent(s) (S¹, S², and S²), and the redox-activesubunit (e.g. porphyrin, chlorin, or ferrocene).

Even more preferred embodiments include the molecules of Formulas XV,XVI, and XVII.

A molecule capable of storing even more information is illustrated inFormula XVIII.

where M is a metal (e.g., Zn, Mg, Cd, Hg, Cu, Ag, Au, Ni, Pd, Pt, Co,Rh, Ir, Mn, B, Al, Ga, Pb, and Sn), F¹, F², and F³ are independentlyselected ferrocenes or substituted ferrocenes, J¹, J², and J³ areindependently selected linkers, K¹, K², K³, and K⁴ are independentlyselected from the group consisting of N, O, S, Se, Te, and CH; L is alinker; and X is selected from the group consisting of a substrate, areactive site that can covalently couple to a substrate, and a reactivesite that can ionically couple to a substrate. In some embodiments, L-Xcan be eliminated and replaced with a substituent (i.e., a ferrocene, asubstituted ferrocene, aryl, phenyl, cycloalkyl, alkyl, halogen, alkoxy,alkylthio, perfluoroalkyl, perfluoroaryl, pyridyl, cyano, thiocyanato,nitro, amino, alkylamino, acyl, sulfoxyl, sulfonyl, imido, amido, andcarbamoyl. Preferred substituents provide a redox potential range ofless than about 5 volts, preferably less than about 2 volts, morepreferably less than about 1 volt. In preferred embodiments, J¹, J², andJ³ are selected from the group consisting of 4,4′-diphenylethyne,4,4′-diphenylbutadiyne, 4,4′-biphenyl, 1-4-phenylene, 4,4′-stilbene,1,4-bicyclooctane, 4,4′-azobenzene, 4,4′-benzylideneaniline, and4,4″-terphenyl.

In certain particularly preferred embodiments, in the molecules ofFormula XVIII, K¹, K², K³ and K⁴ are the same, M is a metal selectedfrom the group consisting of Zn, Mg, Cd, Hg, Cu, Ag, Au, Ni, Pd, Pt, Co,Rh, Ir, Mn, B, Pb, Al, Ga, and Sn, J², J², and J³ are the same; and F¹,F², and F³ are all different. One preferred embodiment is a 5 bitmolecule illustrated by Formula XIX.

In this example, two oxidation states are determined by the porphyrin,and the remaining three states are determined by the three ferrocenes.

Still another preferred embodiment, includes molecules represented byFormula XX:

where K¹, K², K³, and K⁴ are independently selected from the groupconsisting of N, S, O, Se, Te, and CH; M is a metal or (H,H); S¹, S²,and S³ are independently selected from the group consisting of aryl,phenyl, cycloalkyl, alkyl, halogen, alkoxy, alkylthio, perfluoroalkyl,perfluoroaryl, pyridyl, cyano, thiocyanato, nitro, amino, alkylamino,acyl, sulfoxyl, sulfonyl, imido, amido, and carbamoyl; L is present orabsent and, when present, is a linker; and X is selected from the groupconsisting of a substrate, a reactive site that can covalently couple toa substrate, and a reactive site that can ionically couple to asubstrate. In some embodiments L-X can be eliminated and replaced with asubstituent independently selected from the same group as S¹ or S².Preferred substituents (S¹, S², or S³) provide a redox potential rangeof less than about 2 volts. In some preferred variants M is Zn, Mg, Cd,Hg, Cu, Ag, Au, Ni, Pd, Pt, Co, Rh, Ir, Mn, B, Al, Pb, Ga, or Sn. Morepreferably M is Zn, Mg, or (H,H). In some preferred variants, S ismesityl, C₆F₅, 2,4,6-trimethoxyphenyl, or n-pentyl. In some preferredvariants, S¹, S², and S³ are independently CONH(Et), COCH₃, or H. Insome particularly preferred variants, L-X is absent or present, and whenpresent, L-X is 4-(2-(4-mercaptophenyl)ethynyl)phenyl,4-mercaptomethylphenyl, 4-hydroselenophenyl,4-(2-(4-hydroselenophenyl)ethynyl)phenyl, 4-hydrotellurophenyl, or4-(2-(4-hydrotellurophenyl)ethynyl)phenyl.

In some more preferred embodiments of Formula XX, S¹, S², and S³ are allthe same, K¹, K², K³, and K⁴ are all N; and L is p-thiophenyl. M is thenpreferably Zn or (H,H). Particularly preferred variants are listed inTable 2.

TABLE 2 Preferred variants of Formula XX. Variant S¹ and/or S² and/or S³X M 1 Mesityl SCONH(Et) H,H 2 Mesityl SCONH(Et) Zn 3 Mesityl SCOCH₃ H,H4 Mesityl SCOCH₃ Zn 5 Mesityl SH Zn 6 C₆F₅ SCONH(Et) H,H 7 C₆F₅ SH Zn 82,4,6-trimethoxyphenyl SCONH(Et) H,H 9 2,4,6-trimethoxyphenyl SCONH(Et)Zn 10 n-pentyl SCONH(Et) H,H 11 n-pentyl SH ZnIn particularly preferred variants of the compounds indicated in Table2, L can be a phenyl.

Other preferred molecules are illustrated by Formula XXI:

where K¹, K², K³, and K⁴ are independently selected from the groupconsisting of N, O, S, Se, Te, and CH; M is a metal or (H,H); L¹, L²,and L³, and L⁴ are independently present or absent and, when present,are linkers; and X¹, X², X³, and X⁴ are independently selected from thegroup consisting of a substrate, a reactive site that can covalentlycouple to a substrate, and a reactive site that can ionically couple toa substrate. In some embodiments L-X can be eliminated and/or replacedwith a substituent independently selected from various substituents suchas aryl, phenyl, cycloalkyl, alkyl, halogen, alkoxy, alkylthio,perfluoroalkyl, perfluoroaryl, pyridyl, cyano, thiocyanato, nitro,amino, alkylamino, acyl, sulfoxy, sulfonyl, imido, amido, and carbamoyl.Preferred substituents provide a redox potential range of less thanabout 5 volts, preferably less than about 2 volts, more preferably lessthan about 1 volt.

In preferred embodiments, M is Zn, Mg, Cd, Hg, Cu, Ag, Au, Ni, Pd, Pt,Co, Rh, Ir, Mn, B, Pb, Al, Ga, or Sn and in some embodiments, M is morepreferably Zn, Mg, or (H,H). In certain preferred embodiments, L¹-X¹,L²-X², L³-X³, and L⁴-X⁴ are independently present or absent and, whenpresent, are independently 3-mercaptophenyl, 3-mercaptomethylphenyl,3-(2-(4-mercaptophenyl)ethynyl)phenyl,3-(2-(3-mercaptomethylphenyl)ethynyl)phenyl, 3-hydroselenophenyl,3-hydroselenomethylphenyl, 3-(2-(4-hydroselenophenyl)ethynyl)phenyl,3-(2-(3-hydroselenophenyl)ethynyl)phenyl, 3-hydrotellurophenyl,3-hydrotelluromethylphenyl and3-(2-(4-hydrotellurophenyl)ethynyl)phenyl, or3-(2-(3-hydrotellurophenyl)ethynyl)phenyl.

Particularly preferred variants of Formula XXI are illustrated by thecompounds of Formulas XXII, XXIII, and XXIV:

Using the examples and teaching provided herein, one of skill canproduce a virtually limitless supply of data storage molecules suitablefor use in the SHMU storage format of the apparatus of this invention.

C) Dynamic Hole Multi-Unit (DHMU) Storage.

In another embodiment, the data storage medium used in the devices ofthis invention includes one or more molecules that act as a dynamicmulti-unit (DHMU) molecular memory storage. In one embodiment, such astorage molecule comprises a porphyrinic macrocycle containing at leasttwo porphyrins of equal energies held apart from each other at a spacingless than about 50 Å such that said molecule has an odd hole oxidationstate permitting the hole to hop between said two porphyrins and whereinsaid odd hole oxidation state is different from and distinguishable fromanother oxidation state of said porphyrinic macrocycle.

The basic unit of a dynamic hole multi-unit storage molecule isillustrated by Formula XXV.P¹—P²—P³  XXV.where P² is a redox-active subunit having an oxidation potential higherthan P¹ or P³ and P¹ and P³ have the essentially the same oxidationpotential. Thus, when an electron is withdrawn from the molecule, the“hole” does not reside on P¹ and, instead, “hops” from P¹ to P³ and backagain. Data are stored in the “hopping” hole. As will be explainedbelow, this permits interrogation of the molecule without resetting thestate of the molecule. Accordingly, a “read” can be performed without a“refresh”.

One particularly preferred DHMU storage molecule is illustrated byFormula XXVI:

where P¹, P³, P⁴, and P⁶ are independently selected porphyrinicmacrocycles; J¹, J², J³, and J⁴ are independently selected linkers thatpermit electron transfer between the porphyrinic macrocycles; P² and P⁵are independently selected metallo-free porphyrinic macrocycles; and Qis a linker. Preferred “Q” linkers include, but are not limited tolinkers such as 1,4-bis(4-terphen-4″-yl)butadiyne or atetrakis(arylethyne), or linkers comprised of 1,12-carboranyl(C₂B₁₀H₁₂), 1,10-carboranyl (C₂B₈H₁₀), [n]staffane, 1,4-cubanediyl,1,4-bicyclo[2.2.2]octanediyl, phenylethynyl, or p-phenylene units.

One particularly preferred variant of this molecule is illustrated inFormula XXVII.

where M¹ and M² are independently selected metals; S¹, S², S³, S⁴, S⁵,S⁶, S⁷, and S⁸ are independently selected from the group consisting ofaryl, phenyl, cycloalkyl, alkyl, halogen, alkoxy, alkylthio,perfluoroalkyl, perfluoroaryl, pyridyl, cyano, thiocyanato, nitro,amino, alkylamino, acyl, sulfoxyl, sulfonyl, imido, amido, andcarbamoyl; K¹, K², K³, K⁴, K⁵, K⁶, K⁷, and K⁸ are independently selectedfrom the group consisting of are independently selected from the groupconsisting of N, O, S, Se, Te, and CH; L¹ and L² are independentlyselected linkers; and X¹ and X² are independently selected from thegroup consisting of a substrate, a reactive site that can covalentlycouple to a substrate, and a reactive site that can ionically couple toa substrate. Preferred substituents (S¹, S², S³, S⁴, S⁵, S⁶, S⁷ or S⁸)provide a redox potential range of less than about 5 volts, morepreferably less than about 2 volts, and most preferably less than about1 volt. In some embodiments L-X can be eliminated and replaced with asubstituent independently selected from the same group as S¹-S⁸.

In particularly preferred DHMU storage molecules of Formula XXVII, S¹,S², S³, S⁵, S⁶, S⁷, are the same, S⁴ and S⁸ are the same; K¹, K², K³,K⁴, K⁵, K⁶, K⁷, and K⁸ are the same, J¹, J², J³ and J⁴ are the same; andM¹ and M² are different. A preferred species is illustrated by FormulaXXVIII:

The overall architecture of these molecule consists of linear trimers(e.g. like Formula XXV) joined together by a linker (e.g., a1,4-bis(4-terphen-4″-yl)butadiyne or a tetrakis(arylethyne) unit). Insome preferred embodiments, trimers consist of metallo-free base-metalloporphyrins (see, e.g., Formula XVIII).

In preferred embodiments, the peripheral porphyrins in a given trimerhave identical metals and substituents engendering equivalent redoxpotentials. The core free base porphyrins each have perfluorophenylsubstituents to render the porphyrins more resistant to oxidation. Thecentral linker (e.g., a 1,4-bis(4-terphen-4″-yl)butadiyne or atetrakis(arylethyne)) serves as a structural unit to hold the trimerstogether. In addition, each porphyrin bears a linker (e.g., ap-thiophenol unit) for assembly on electroactive surfaces. Thisnanostructure, although complex in appearance, is in fact substantiallysmaller than other nanostructures synthesized and known in the priorart.

Information is stored in the dynamic hole memory via oxidation of theporphyrinic macrocycles as described above for the static-hole memory.However, there are certain key differences that distinguish the twotypes of memory elements that are illustrated by reference to FormulaXXVIII. In compounds of Formula XXVIII, the oxidation potentials of thetwo Mg porphyrins are essentially identical to one another (thedifference is less than thermal energy at room temperature), as is alsothe case for the two Zn porphyrins. Thus, oxidation results in thefollowing sequence of states: [MgP₁ ⁺, others neutral], [MgP₁ ⁺, MgP₂ ⁺,both ZnP₃ and ZnP₄ neutral], [MgP₁ ⁺, MgP₂ ⁺, ZnP₃ ⁺, ZnP₄], [MgP₁ ⁺,MgP₂ ⁺, MgP₃ ⁺, ZnP₄ ⁺], [MgP₁ ⁺⁺, MgP₂ ⁺, ZnP₃ ⁺, ZnP₄ ⁺], and so forthuntil two holes have been removed from each metalloporphyrin, i.e. [MgP₁⁺⁺, MgP₂ ⁺⁺, ZnP₃ ⁺⁺, ZnP₄ ⁺⁺]. Thus, up to eight holes can again bestored in the nanostructure.

However, the cases where one hole (or three holes) resides on either theMg or the Zn porphyrins are unique. For these odd-hole oxidation states,the hole(s) rapidly hop between the two metalloporphyrins (100's of KHzto 100's of MHz, depending on the type of porphyrin. In contrast, wheneach Mg or Zn porphyrin contains the same number of holes, no hoppingcan occur.

In a preferred embodiment, information is stored only via thehole-hopping states of the multiporphyrin nanostructure, hence thedesignation “dynamic-hole” multi-unit storage. The encoding of aprototypical DHMU storage cell using the hole-hopping states is shown inFIG. 5 (the double-headed arrows indicate hole hopping). The syntheticmethodologies already established permit extension of the architecturevia addition of other trimeric units wherein the oxidation potential ofthe metalloporphyrin is different from that of the others, thusincreasing the dynamic range of the basic memory element beyond thatshown.

D) Tightly Coupled Storage Molecules.

As indicated above, the use of tightly coupled subunits permits thecreation of a storage molecule/storage medium having multiple differentand distinguishable non-neutral oxidation states. In particular, thejuxtaposition of the subunits at a spacing that permits strong (tight)coupling between the two subunits results in a splitting of the redoxpotentials of the structurally identical units. In this manner,identical porphyrins can be used in the construction of a storagemolecule capable of storing many bits of information thereby resultingin substantial efficiencies in the construction of storage media.

This is illustrated with respect to a porphyrin. A monomeric porphyrinhas three accessible oxidation states (neutral, mono-cation, dication),the precise level of which can be tuned through synthetic variation ofperipheral substituents, central metal, and use of skeletal atoms otherthan nitrogen.

One example of a tightly coupled dimeric porphyrin array that-we haveinvestigated is shown below in Formula XXIX (porphyrin dimer XXIX). Thismolecule has two zinc porphyrins linked to each other at the porphyrinmeso-positions.

The synthesis of this porphyrin dimer was accomplished using methods forpreparing building block porphyrins (Cho et al. (1999) J. Org. Chem. 64:7890-7901).

Electrochemical examination of porphyrin dimer XXIX revealed oxidationwaves at +0.49 and +0.66 V for the formation of the monocation of thetwo porphyrins comprising the porphyrin dimer. This is in contrast tothe single oxidation wave for the corresponding porphyrin monomer whichis expected at +0.58 V. The appearance of two waves in porphyrin dimerXXIX indicates that the oxidation of the first porphyrin forming themonocation shifts the potential of the second porphyrin to higherpotential. This shift in potential provides the opportunity to accessdistinct and different oxidation potentials in a multiporphyrin arraywhere each porphyrin is identical. In this example, the porphyrin dimerI has four non-zero oxidation states as illustrated in Table 3.

TABLE 3 Oxidation potentials observed in porphyrin dimer XXIX. Oxidationpotential (V) Redox-active unit 0.49 dimer oxidation potential 1 0.66dimer oxidation potential 2 0.95 dimer oxidation potential 3 1.03 dimeroxidation potential 4In this example, four different and distinguishable non-zero oxidationstates are available in the resulting dimer, but construction of thestorage molecule required synthesis of only a single subunit (porphyrinmonomer). This dramatically reduces the complexity and cost of thecreation of suitable storage molecules for use in the storage devices ofthis invention.

The principle is generalizable. One is not limited to the constructionof tightly coupled dimers. It is also possible to construct tightlycoupled trimers and longer oligomers having more different anddistinguishable oxidation states.

In addition, the constituent subunits need not be limited to porphyrins.Essentially any molecule that has multiple different and distinguishableoxidation states and that can be tightly coupled to produce moleculeshaving even more different and distinguishable oxidation states can beused as a subunit. Such molecules include, but are not limited to aporphyrinic macrocycle, a metallocene (e.g. a ferrocene), a linearpolyene, a cyclic polyene, a heteroatom-substituted linear polyene, aheteroatom-substituted cyclic polyene, a tetrathiafulvalene, atetraselenafulvalene, a metal coordination complex, a buckyball, atriarylamine, a 1,4-phenylenediamine, a xanthene, a flavin, a phenazine,a phenothiazine, an acridine, a quinoline, a 2,2′-bipyridyl, a4,4′-bipyridyl, a tetrathiotetracene, a peri-bridged naphthalenedichalcogenide, and the like.

A pair of subunits is said to be strongly coupled when coupling of thesubunits (e.g. porphyrins) increases the number of distinct anddistinguishable oxidation states above the number of oxidation statesavailable in the separate pair of subunits. In the case of the dimer ofFormula I, the two separate subunits each have one non-zero oxidationstate, but the dimer has four non-zero oxidation states and is thusessentially strongly coupled for the purposes of this invention.

Tight coupling is typically achieved by directly covalently linking thetwo subunits. In certain, instances, however, the subunits may be joinedby a linker and/or joined by coordination to a metal, as long as thesubunits are positioned closely enough together that they arefunctionally “tightly coupled.” One example of subunits tightly coupledby coordination to a metal is provided by the lanthanide porphyrinic“sandwich” molecules. These include, but are not limited, to a varietyof double-decker and triple-decker sandwich molecules comprised ofporphyrinic molecules and metals (e.g. metals of the lanthanide seriessuch as La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and Ywhich has properties similar to lanthanides) (see, e.g., Jiang et al.(1997) Inorg. Chim. Acta, 255: 59-64; Ng and Jiang (1997) J. Chem. Soc.Rev., 26: 433-442; Chabach et al. (1996) Angew. Chem. Int. Ed. Engl.,35: 898-899). Sandwich structures have also been made using Zr, Hf, Th,and U.

Methods of determining when molecules are tightly coupled are well knownto those of skill in the art. Using optical spectrographic methods,tightly coupled molecules will be revealed as perturbations in theoptical spectra of the tightly coupled molecule. Thus, typically when anelectron is removed from the system it will typically be accompanied anelectronic transition (mixed valence transition).

Similarly when examining the vibrational spectrum of the system (e.g.via infrared or raman spectroscopy) a weakly coupled system shows aneutral and a cation signature. As the system becomes more tightlycoupled, the neutral and cation signature diminish and the system showsa characteristic signature at a frequency between the neutral and thecation frequency (Donohoe et al. (1988) J. Am. Chem. Soc., 110:6119-6124). It is understood that the subunits could be so tightlycoupled that the redox processes are those of a single supermolecule.

In a preferred embodiment, the system is designed to provide multipledistinct and distinguishable oxidation states in a redox potential rangeof less than about 5 volts, preferably less than about 2 volts, morepreferably less than about 1 volt. While the oxidation states aredifferent and distinguishable at a difference of at least 1 mV,preferably at least 5 mV, and more preferably at least 10 mV, inparticularly preferred embodiments, the oxidation states are separatedfrom each other by at least about 25 mV, preferably by at least 50 mV,more preferably by at least about 100 mV, and most preferably by atleast about 130-150 mV.

As indicated above, in certain preferred embodiments, the storagemolecules of this invention are polymeric molecules comprising two ormore monomeric subunits. In particularly preferred embodiments thesubunits are identical or perhaps differ only in the presence or absenceof a linker for attachment to the electrode. Use of essentiallyidentical subunits substantially reduces the synthetic chemistryrequired to produce a storage device resulting in substantially moreefficient and less error-prone device assembly and substantial savingsof labor and cost.

In this approach, preferred subunits (monomers comprising the multimeric(array) molecule are porphyrinic macrocycles or metallocenes withporphyrinic macrocycles being most preferred. In one particularlypreferred embodiments, a pair of the tightly coupled subunits has thefollowing structure shown in Formula XXX:

where S¹, S², S³, and S⁴ are substituents independently selected fromthe group consisting of aryl, phenyl, cycloalkyl, alkyl, halogen,alkoxy, alkylthio, perfluoroalkyl, perfluoroaryl, pyridyl, cyano,thiocyanato, nitro, amino, alkylamino, acyl, sulfoxyl, sulfonyl, imido,amido, and carbamoyl and the substituents provide a redox potentialrange of less than about 2 volts. Alternatively, one or more of S¹, S²,S³, and S⁴ are -L-X where -L-X, when present is optionally present onone or both subunits and L, when present, is a linker; X is selectedfrom the group consisting of a substrate, a reactive site that cancovalently couple to a substrate, and a reactive site that can ionicallycouple to a substrate; M is a metal; and K¹, K², K³, and K⁴ areindependently selected from the group consisting of N, O, S, Se, Te, andCH. In certain preferred embodiments, S¹, S², and S³ are independentlyselected from the group consisting of mesityl, C₆F₅,2,4,6-trimethoxyphenyl, phenyl, p-tolyl, p-(tert-butyl)phenyl,3,5-dimethylphenyl, 3,5-di(tert-butyl)phenyl, 3,5-dimethoxyphenyl,3,5-dialkoxyphenyl, and n-pentyl. In certain preferred embodiments, -L-Xis selected from the group consisting4-(2-(4-mercaptophenyl)ethynyl)phenyl, 4-mercaptomethylphenyl,4-hydroselenophenyl, 4-(2-(4-hydroselenophenyl)ethynyl)phenyl,4-hydrotellurophenyl, 2-(4-mercaptophenyl)ethynyl,2-(4-hydroselenophenyl)ethynyl, 2-(4-hydrotellurophenyl)ethynyl, and4-(2-(4-hydrotellurophenyl)ethynyl)phenyl. Of course, the molecule neednot be a dimer, in which case one or more of S¹, S², S³, or S⁴ canindependently be another subunit.

In a particularly preferred embodiment, S¹ and S³ are both the same; andK¹, K², K³, and K⁴ are all the same (e.g. N). Various preferredembodiments are listed above in Formula XXIX and below in Formulas XXXI,XXXII, XXXIII, and XXXIV.

Information is stored in the storage molecule by removing electrons fromthe porphyrin constituents (leaving a hole and forming a π-cationradical (Strachan et al. (1997) J. Am. Chem. Soc., 119: 11191-11201; Liet al. (1997) J. Mater. Chem. 7: 1245-1262, and Seth et al. (1996) J.Am. Chem. Soc. 118: 11194-11207; Seth et al. (1994) J. Am. Chem. Soc.116: 10578-10592). The redox characteristics of the subunits areadjusted by selection of the metal (M) and the substituents (e.g. S¹,S², S³).

The synthetic methodologies already established permit the extension ofthe linear architecture, thus increasing the dynamic range of this basicmemory element well beyond the four bits indicated in Table 3. Inaddition, subunits can be engineered that have more than two oxidationstates and more complex subunits can be utilized (e.g. subunits eachcomprising a porphyrinic macrocycle coupled to a metallocene). Thus forexample, molecules and/or subunits can be engineered that have virtuallyany number (e.g., 2, 4, 8, 16, 32, 64, 128, etc.) of different anddistinguishable oxidation states.

V. Synthesis and Characterization of Storage Medium Molecule(s).

A) Designing Oxidation States into the Storage Medium Molecule(s).

Control over the hole-storage and hole-hopping properties of theredox-active units of the storage molecules used in the memory devicesof this invention allows fine control over the architecture of thememory device.

Such control is exercised through synthetic design. The hole-storageproperties depend on the oxidation potential of the redox-active unitsor subunits that are themselves or are that are used to assemble thestorage media used in the devices of this invention. The hole-storageproperties and redox potential can be tuned with precision by choice ofbase molecule(s), associated metals and peripheral substituents (Yang etal. (1999) J. Porphyrins Phthalocyanines, 3: 117-147).

For example, in the case of porphyrins, Mg porphyrins are more easilyoxidized than Zn porphyrins, and electron withdrawing or electronreleasing aryl groups can modulate the oxidation properties inpredictable ways. Hole-hopping occurs among isoenergetic porphyrins in ananostructure and is mediated via the covalent linker joining theporphyrins (Seth et al. (1994) J. Am. Chem. Soc., 116: 10578-10592, Sethet al (1996) J. Am. Chem. Soc., 118: 11194-11207, Strachan et al. (1997)J. Am. Chem. Soc., 119: 11191-11201; Li et al. (1997) J. Mater. Chem.,7: 1245-1262, Strachan et al. (1998) Inorg. Chem., 37: 1191-1201, Yanget al. (1999) J. Am. Chem. Soc., 121: 4008-4018). Hole-hopping is notexpected in the SHMU storage molecule(s) because each porphyrin has adifferent oxidation potential. Hole-hopping is expected amongisoenergetic porphyrins in the DHMU molecule(s).

We have studied hole-hopping phenomena extensively in relatednanostructures in solution. We also have prepared and characterized theelectrochemical properties of a library of monomeric Mg or Zn porphyrinsbearing diverse aryl groups (Yang et al. (1999) J. PorphyrinsPhthalocyanines, 3: 117-147). The effects of metals on metalloprophyrinoxidation potentials are well known (Fuhrhop and Mauzerall (1969) J. Am.Chem. Soc., 91: 4174-4181). Together, these provide a strong foundationfor designing devices with predictable hole-storage and hole-hoppingproperties.

The design of compounds with predicted redox potentials is well known tothose of ordinary skill in the art. In general, the oxidation potentialsof redox-active units or subunits are well known to those of skill inthe art and can be looked up (see, e.g., Handbook of Electrochemistry ofthe Elements). Moreover, in general, the effects of various substituentson the redox potentials of a molecule are generally additive. Thus, atheoretical oxidation potential can be readily predicted for anypotential data storage molecule. The actual oxidation potential,particularly the oxidation potential of the information storagemolecule(s) or the information storage medium can be measured accordingto standard methods. Typically the oxidation potential is predicted bycomparison of the experimentally determined oxidation potential of abase molecule and that of a base molecule bearing one substituent inorder to determine the shift in potential due to that particularsubstituent. The sum of such substituent-dependent potential shifts forthe respective substituents then gives the predicted oxidationpotential.

In addition, the oxidation potential shift produced by tightly couplingthe molecules can be predicted by methods well known to those of skillin the art (see, e.g., Citation). The actual oxidation states can beempirically determined as described herein.

B) Synthesis of Storage Medium Molecules.

The basic synthetic methodologies used to construct the storage mediummolecules of this invention are described in Prathapan et al. (1993) J.Am. Chem. Soc., 115: 7519-7520, Wagner et al. (1995) J. Org. Chem., 60:5266-5273, Nishino et al. (1996) J. Org. Chem., 61: 7534-7544, Wagner etal. (1996) J. Am. Chem. Soc., 118: 11166-11180, Strachan et al. (1997)J. Am. Chem. Soc., 119: 11191-11201, and Li et al. (1997) J. Mater.Chem., 7: 1245-1262. These papers describe various strategies for thesynthesis of a number of multi-porphyrin (porphyrinic macrocycle)compounds. More particularly, these papers which focus on light capture,energy funneling, and optical gating, has led to the preparation ofnanostructures containing up to 21 covalently linked porphyrins (Fenyoet al. (1997) J. Porphyrins Phthalocyanines, 1: 93-99, Mongin et al.(1998) J. Org. Chem., 63: 5568-5580, Burrell and Officer (1998) Synlett1297-1307, Mak et al. (1998) Angew. Chem. Int. Ed. 37: 3020-3023, Nakanoet al. (1998) Angew. Chem. Int. Ed. 37: 3023-3027, Mak et al. (1999)Chem. Commun., 1085-1086). Two-dimensional architectures, such asmolecular squares (Wagner et al. (1998) J. Org. Chem., 63: 5042-5049),T-shapes (Johnson, T. E. (1995), Ph.D. Thesis, Carnegie MellonUniversity), and starbursts (Li et al. (1997) J. Mater. Chem., 7:1245-1262) all comprised of different covalently linked porphyrinconstituents, have also been prepared.

In addition, the hole storage and dynamic hole mobility characteristicsof the multiporphyrin nanostructures have been investigated in detailduring the course of our other studies of these materials (Seth et al.(1994) J. Am. Chem. Soc., 116: 10578-10592, Seth et al (1996) J. Am.Chem. Soc., 118: 11194-11207, Strachan et al. (1997) J. Am. Chem. Soc.,119: 11191-11201; Li et al. (1997) J. Mater. Chem., 7: 1245-1262,Strachan et al. (1998) Inorg. Chem., 37: 1191-1201, Yang et al. (1999)J. Am. Chem. Soc., 121: 4008-4018).

The general synthetic strategy preferably involves the followingapproaches: (1) a synthesis of the subunit(s) comprising the storagemolecules of this invention; (2) coupling of the subunits, if necessary,to form the polymeric storage molecules; and (3) the directedself-assembly of the resulting structures on electrode (e.g. goldelectrode) surfaces.

The methods for synthesis, purification, and characterization for themolecular memory molecules (MMMs) generally follow those employed in themodular stepwise synthesis (Lindsey et al. (1994) Tetrahedron, 50:8941-8968) of molecular wires (Wagner et al. (1994) J. Am. Chem. Soc.,116: 9759-9760), optoelectronic gates (Wagner et al. (1996) J. Am. Chem.Soc., 118: 3996-3997) and light-harvesting nanostructures (Prathapan etal. (1993) J. Am. Chem. Soc., 115: 7519-7520, Johnson, T. E. (1995),Ph.D. Thesis, Carnegie Mellon University, Wagner et al. (1996) J. Am.Chem. Soc., 118: 11166-11180, Li et al. (1997) J. Mater. Chem., 7:1245-1262, and Li et al. (1998) J. Am. Chem. Soc., 120: 10001-10017). Incertain preferred embodiments, the following synthetic methods form thefoundation for the building block synthesis of porphyrin buildingblocks:

(1) A room temperature one-flask synthesis of meso-substitutedporphyrins (Lindsey et al. (1987) J. Org. Chem. 52: 827-836, Lindsey etal. (1994) J. Org. Chem. 59: 579-587, Li et al. (1997) Tetrahedron, 53:12339-12360.).

(2) Incorporation of bulky groups around the porphyrin to achieveenhanced solubility in organic solvents (Lindsey and Wagner (1989) J.Org. Chem., 54: 828-836).

(3) A one-flask synthesis of dipyrromethanes, key building blocks in thesynthesis of porphyrins bearing 2-4 different meso-substituents (Lee andLindsey (1994) Tetrahedron, 50: 11427-11440, Littler et al. (1999) J.Org. Chem. 64: 1391-1396).

(4) A synthesis of trans-substituted porphyrins without acidolyticscrambling (Littler et al. (1999) J. Org. Chem. 64: 2864-2872)/

(5) A rational synthesis of porphyrins bearing up to 4 differentmeso-substituents (Lee et al. (1995) Tetrahedron, 51: 11645-11672, Choet al. (1999) J. Org. Chem. 64: 7890-7901)/

(6) Mild methods for inserting magnesium (Lindsey and Woodford (1995)Inorg. Chem. 34: 1063-1069, O'Shea et al. (1996) Inorg. Chem., 35:7325-7338) or other metals (Buchler, J. W. In The Porphyrins; Dolphin,D. Ed.; Academic Press: New York. 1978; Vol. I, pp. 389-483) intoporphyrins.

(7) A general approach for preparing thiol-derivatized porphyrinbuilding blocks including various protecting groups for the thiol moiety(Gryko et al. (1999) J. Org. Chem. 64: 8634-8647).

In one embodiment, building blocks are synthesized using methodsdescribed by Wagner et al. (1996) J. Am. Chem. Soc., 118: 11166-11180,Strachan et al. (1997) J. Am. Chem. Soc., 119: 11191-11201,Wagner et al.(1996) J. Am. Chem. Soc., 118: 3996-3997, Li et al. (1997) J. Mater.Chem., 7: 1245-1262; Lindsey et al. (1994) Tetrahedron, 50: 8941-8968;Wagner et al. (1994) J. Am. Chem. Soc., 116: 9759-9760; Lindsey andWagner (1989) J. Org. Chem., 54: 828-836; Lee and Lindsey (1994)Tetrahedron, 50: 11427-11440; Lee et al. (1995) Tetrahedron, 51:11645-11672; Lindsey and Woodford (1995) Inorg. Chem. 34: 1063-1069; andWagner et al. (1995) J. Org. Chem., 60: 5266-5273.

The synthesis of the molecules that form the basis for the storagemolecules (e.g., SHMU storage molecules, DHMU storage molecules, etc.)is performed using a modular building block approach. This approachemploys a stepwise synthesis (rather than polymerization) and yieldshighly purified and well-characterized products. One approach, utilizesa series of redox-active “building blocks” (e.g., a series of monomericporphyrinic macrocycles or ferrocene constituents) that can be linked tothe gold substrate that will serve as one of the electrodes in the chip.Preferred monomeric redox-active units that are prepared have differentoxidation potentials that fall in the range from 0 to 1.3 volts.

The two different redox-active units can be linked together to form abasic dimeric architecture. Similarly, two other different redox-activeunits (e.g. porphyrins) can be linked to form a second dimericarchitecture. Then the two dimers can be linked to form a linear, ornon-linear, tetrameric architecture consisting of four different typesof redox-active units (e.g., porphyrins).

One example of a preferred synthesis approach is shown in FIG. 6. Thereaction of 5-mesityldipyrromethane (Lee and Lindsey (1994) Tetrahedron,50: 11427-11440) with two aldehydes affords three porphyrins, includingthe desired mono-thiol porphyrin. The latter is metalated with Zn or Mg,and then the thiol protecting group can be removed. Of the various thiolprotecting groups (Hsung et al. (1995) Tetrahedron Lett., 36: 4525-4528;Ricci et al. (1977) J. Chem. Soc. Perkin Transactions I., 1069-1073) theS-acetyl or S—(N-ethyl-carbamoyl) group is stable toward the requiredsynthetic conditions yet cleaved easily with methanolic diethylamine.The useful precursor 4-mercaptobenzaldehyde is readily available (Younget al. (1984) Tetrahedron Lett., 25: 1753-1756). The resulting porphyrinmono-thiol can be assembled on a gold surface, or the protected thiolcan be deprotected in situ on a gold surface.

The synthesis of an SHMU storage molecule is shown in FIG. 7. Fourporphyrin building blocks are employed in the synthesis of thisnanostructure. Each building block is available via establishedsynthetic routes (either via the route we established forABCD-porphyrins or via a 3+1 route involving a tripyrrane) (Lee et al.(1995) Tetrahedron, 51: 11645-11672). The fundamental methodology forjoining the porphyrin building blocks involves Pd-mediated coupling ofan ethynyl-porphyrin and an iodo-porphyrin (Wagner et al. (1995) J. Org.Chem., 60: 5266-5273). Our optimized conditions for these couplingreactions afford 60-80% yields in 2-4 h. Purification is achieved usingsize-exclusion chromatography and characterization is accomplished withlaser desorption mass spectrometry (see, e.g., Fenyo et al. (1997) J.Porphyrins Phthalocyanines, 1: 93-99). This synthetic route is toleranttoward diverse aryl groups and metals in the porphyrin unit.

The stepwise synthesis makes available the dimeric unit of the SHMUstorage molecule upon one cycle of coupling. The dimer will be examinedelectrochemically. Following cleavage of the S-acetyl protecting group,the thiols may undergo oxidative coupling (forming the disulfides)during handling and processing. Such disulfides can be reduced toregenerate the thiols, or deposited on gold surfaces whereupon reductionin situ yields the bound thiol species. Alternatively, the S-acetylgroups can be cleaved in situ upon exposure to the metal (e.g., gold)surface (Tour et al. (1995) J. Am. Chem. Soc., 117: 9529-9534). A numberof porphyrin thiols have been prepared and deposited on metals but notfor memory storage applications (see, e.g., Zak et al. (1993) Langmuir,9: 2772-2774; Hutchison et al. (1993) Langmuir 9: 3277-3283; Bradshaw etal. (1994) Gazz. Chim. Ital. 124, 159-162; Postlethwaite et al. (1995)Langmuir, 11: 4109-4116; Akiyama et al. (1996) Chem. Lett, 907-908;Uosaki et al. (1997) J. Am. Chem. Soc., 119: 8367-8368; Katz and Willner(1997) Langmuir, 13: 3364-3373; Ishida et al. (1998) Chem. Lett.,267-268; Ishida et al. (1998) Chem. Commun., 57-58). Nanostructureshaving up to 21 porphyrins are readily synthesized.

A representative synthesis of a DHMU storage molecule is shown in FIG.8. Three porphyrin building blocks are prepared and metalated withmagnesium or zinc. The synthetic strategy builds the two arms of theDHMU storage molecule separately, which are then coupled in thepenultimate step of the synthesis. Each arm is constructed via twoPd-mediated couplings, yielding the respective trimers. One trimer isiodinated at the ethyne (Barluenga et al. (1987) Synthesis, 661-662; andBrunel and Rousseau (1995) Tetrahedron Lett., 36: 2619-2622) then joinedwith the other trimer in a heterocoupling process to form the H-likestructure. A variety of conditions can be employed for theheterocoupling reaction (Alami and Ferri (1996) Tetrahedron Lett., 37:2763-2766). We previously showed that Pd-mediated (copper-free)couplings can be employed for homocoupling reactions (Wagner et al.(1995) J. Org. Chem., 60: 5266-5273). Copper-free couplings arepreferred to avoid copper insertion in the free base porphyrin. Here thesame Pd-mediated coupling is used to perform the heterocoupling. Thefinal step is cleavage of the S-acetyl protecting group, which proceedsin methanolic Et₂NH. Such conditions do not alter any of the otherfunctionalities in the molecule. Alternatively, the S-acetyl groups canbe cleaved in situ upon exposure to the metal (e.g., gold) surface (Touret al. (1995) J. Am. Chem. Soc., 117: 9529-9534).

General methods for joining porphyrin monomers to form linked porphyrinarrays (e.g. meso-meso linked porphyrins) are described by Osuka andShimidzu (1997) Angew. Chem. Int. Ed. Engl. 36: 135-137, Yoshida et al.(1998) Chem. Lett. 55-56, Nakano et al. (1998) Angew. Chem. Int. Ed. 37:3023-3027, Ogawa et al. (1998) Chem. Commun. 337-338, Ogawa et al.(1999) Angew. Chem. Int. Ed. 38: 176-179, and Senge and Feng (1999)Tetrahedron Lett. 40: 4165-4168. Using the synthesis strategiesexemplified here and in the Examples, one of ordinary skill in the artcan routinely produce relatively complex data storage molecules for usein the devices of this invention.

Using the synthesis strategies exemplified here and in the Examples, oneof ordinary skill in the art can routinely produce relatively complexdata storage molecules for use in the devices of this invention.

C) Characterization of the Storage Media.

The storage media molecule(s), once prepared, can be characterizedaccording to standard methods well known to those of skill in the art.The characterization of multiporphyrin nanostructures has been described(see, e.g., Strachan et al. (1997) J. Am. Chem. Soc., 119: 11191-11201;Wagner et al. (1996) J. Am. Chem. Soc., 118: 3996-3997; Li et al. (1997)J. Mater. Chem., 7.: 1245-1262; Seth et al. (1996) J. Am. Chem. Soc.,118: 11194-11207; Seth et al. (1994) J. Am. Chem. Soc., 116:10578-10592). In a preferred embodiment, the electrochemical studiesinclude cyclic and square-wave voltammetry to establish the redoxpotentials of the monomeric and multi-unit constituents of the storagemedia. Bulk electrochemical oxidations are performed on each of thestorage materials to assess the hole-storage capabilities and thestability. Absorption and vibrational spectroscopic methods are used toassess the structural and electronic properties of both the neutral andoxidized materials. Electron paramagnetic resonance techniques are usedto probe the hole-storage and hole-mobility characteristics of theoxidized storage molecules. Using the above-identified techniques,benchmarks for the expected performance characteristics of a storagemolecule (e.g., oxidation potentials, redox reversibility, dynamichole-mobility characteristics, etc.) can be ascertained.

D) Self-Assembly of the Storage Medium Molecules on Target Substrates.

In preferred embodiments, the storage molecules comprising the storagemedium are designed to self-assemble on a substrate (e.g. a metal suchas gold). The disk-like structure of the porphyrin macrocycles engendersself-assembly. Self-assembled monolayers of porphyrins on solidsubstrates are well known and have been extensively studied (see, e.g.,Schick et al. (1989) J. Am. Chem. Soc., 111: 1344-1350, Mohwald et al.(1986) Thin Solid Films, 141: 261-275).

To exert control over the pattern of self-assembly, reactive sites (e.g.thiols) or linkers bearing active sites are incorporated into thestorage molecules (nanostructures). The reactive sites bind to thetarget (e.g. gold electrode) surface giving an organized self-assembledstructure. In the case of porphyrins with thiol linkers attached to themeso-positions, the porphyrins arrange in upright orientations.Non-covalent interactions between storage molecules are typically weak,particularly when bulky aryl groups are attached to each of theporphyrins.

VI. Writing to the Storage Device.

In preferred embodiments of the data storage devices of this invention,information is written to a particular memory location via applicationof a potential of the requisite value and temporal duration at theappropriate working and reference electrode(s) to achieve the desireddigital value. The information can be erased via application of apotential of the opposite sign.

The writing process is illustrated with respect to storage of data in astatic hole multi-unit storage molecule (SHMU storage molecule). Oneparticular such molecular memory is illustrated by Formula IX and thewriting process is summarized below in Table 4.

As shown in Table 4, each porphyrin has two redox processes, each ofwhich is separated by at least 150 mV. To activate bit 001, a potentialgreater than 0.38 V (but less than 0.51 V) would be applied to thememory element to oxidize the magnesium porphyrin to its first oxidationstate. The other porphyrins in the S U storage molecule could then besequentially oxidized through the various redox states to provide thedifferent bits. In preferred embodiments, this is accomplished throughthe application of very short (e.g., microsecond) pulses applied at avoltage sufficient to oxidize a porphyrin to the appropriate redoxstate. This process is summarized in FIG. 9. Thus, each redox state ofthe composite porphyrinic nanostructure can independently accessed toprovide one bit of resolution. This can be accomplished via theelectrochemical oxidation of the molecule in stepwise increments.

TABLE 4 Redox properties of model metalloporphyrins (MP). Bit Redoxprocess E⁰ (V vs. Ag/AgCl) 000 All redox components in neutral state 001MgPZnP

MgP⁺ZnP + 1 e⁻ 0.38 010 MgP⁺ZnP

MgP⁺ZnP⁺ + 1 e⁻ 0.51 011 MgP⁺ZnP⁺

MgP²⁺ZnP⁺ + 1 e⁻ 0.71

Another example of the writing process is illustrated with respect tostorage of data in porphyrin dimer XXIX (Formula XXIX). While eachporphyrin subunit individually has a single non-neutral oxidation state,as shown in Table 5, the dimer has four non-zero oxidation states, eachof which is separated by at least about 50 mV. To activate bit

TABLE 2 Mapping of bits onto oxidation potential in the porphyrin dimerof Formula I. Bit Oxidation potential (V) Redox-active unit parity 0dimer neutral 00 0.49 dimer oxidation potential 1 01 0.66 dimeroxidation potential 2 10 0.95 dimer oxidation potential 3 00 1.03 dimeroxidation potential 4001, a potential greater than 0.49 V (but less than 0.66 V) would beapplied to the memory element to oxidize porphyrin 1 to its firstoxidation state. A voltage greater than 0.66 V and less than 0.95 Vwould oxidize porphyrin 1 to its second oxidation state. A voltagegreater than 0.95 V and less than 1.03 V would oxidize porphyrin 2 ofthe dimer to its first oxidation state and a voltage greater than 1.03would oxidize porphyrin 2 of the dimer to its second oxidation state.

There is a great advantage to the small size of each memory element,which is essentially a modified electrode surface. When each memoryelement is reduced to sub-micron dimensions, the area of the surfaceallows the presence of only a few hundred data storage (e.g., porphyrin)molecules. Using Faraday's law, Q=nFN (where Q equals the total charge,n equals the number of electrons per molecule, F is 96,485 Coulombs/moleand N is the number of moles of electroactive species present), it canbe determined that only a small charge (1.6×10⁻¹⁶ C; if passed in 1 μs,would result in a current of roughly 160 pA) must pass in order tochange the electrochemical charge corresponding to each bit.

Additionally, the intrinsic limitation to the speed of mostelectrochemical experiments lies in the time required to charge theelectrode to the appropriate potential (the charging current, which hasa time dependence of exp(−t/RC)). Since the capacitance of the electrodeis directly proportional to its area, miniaturization of each element ofthe system to submicron dimensions will greatly increase its speed. Forexample, a square gold electrode with 0.1 μm dimensions would have acapacitance of approximately 2×10⁻¹⁹ F, leading to an RC time constantof only 2 picoseconds. For this reason, electrode charging currentsshould be insignificant in determining the ultimate performance of thesedevices.

The voltage used to write the data can be derived from any of a widevariety of sources. In a simple embodiment, the voltage can simply bethe output from a power supply. However, in preferred embodiments, thevoltage will be the output from some element of an electronic circuit.The voltage can be a signal, the representation of a logic state, theoutput from a gate, from an optical transducer, from a centralprocessing unit, and the like. In short, virtually any voltage sourcethat can be electrically coupled to the devices of this invention can beused to write data to the storage media therein.

VII. Reading from the Storage Device.

The storage device(s) of this invention can be read according to any ofa wide variety of methods well known to those of ordinary skill in theart. Essentially any method of detecting the oxidation state of acompound can be utilized in the methods of this invention. However,where the readout is destructive of the state of the memory cell(s)(e.g. in certain SHSU or SHMU memories), the read will preferably befollowed by a refresh to reset the oxidation state of the storage cell.

In particularly preferred embodiments, the storage medium 102 of astorage cell 100 is set to neutral (e.g., 0 potential for the system,but which might not be at true zero voltage with respect to ground)using the working electrode. The oxidation state of the memory cell isthen set by changing the potential at the reference electrode 103 (e.g.by setting the reference electrode negative to the desired voltage). Theoxidation state of the storage cell is then measured (e.g. usingsinusoidal voltammetry) via the working electrode 101. In this preferredformat, the oxidation state is assayed by measuring current. Bymeasuring current at the working electrode 101 and setting the statewith the reference electrode 103, the measurement is not made at theplace the potential is applied. This makes it far simpler todiscriminate the oxidation state. If the potential were applied to theelectrode through which the current was measured unnecessary noise wouldbe introduced into the system.

A) Reading from Static Hole Storage Media.

In the case of static hole storage media (e.g. SHSU and SHMU), thereading of information from a particular memory location is achievedextremely rapidly by sweeping a potential over the full range used toestablish the dynamic range of the storage element. The fidelity of themeasurement is dependent on how well the oxidation state of theindividual storage element can be determined. Traditionally,electrochemical methods could only improve the signal to noise ratio bydiscriminating the faradaic signal from the background components in thetime domain through application of pulse waveforms (i.e., differentialpulse polarography, square wave voltammetry). These methods discriminatethe faradaic current from the charging current in the time domain, sincecharging currents decay much more rapidly than the faradaic current(exp(−t/RC) vs t^(−1/2), respectively). However, the analytical faradaiccurrent is not totally discriminated from the charging current, and mostof the signal is discarded because sampling is done late in the pulsecycle.

More recently, sinusoidal voltammetry (SV) has been shown to havesignificant advantages over traditional waveforms in an electrochemicalexperiment (Singhal et al. (1997) Anal. Chem., 69:1662-1668. Forexample, the background current resulting from cyclic voltammetry(consisting primarily of charging current) resembles a square wave,which contains significant intensity at both fundamental and oddharmonic frequencies. In contrast, the charging current resulting fromsine wave excitation has only one frequency component centered at thefundamental, while the faradaic current is distributed over manyfrequencies as is illustrated in FIG. 10. This characteristic of sinewave excitation simplifies the electroanalytical measurement, since thesignal from each oxidation state can be fine-tuned by “locking-in” onone of the higher frequency harmonics. Ultimately, the speed at whichthis can be performed is only limited by the kinetics of the redoxreaction, which may ultimately lead to megahertz frequency operation.

Since most electrochemical methods rely on differences between theE_(1/2)'s (E_(1/2) is the potential at which half of the subjectmolecules are oxidized or reduced to a particular oxidation state) todifferentiate compounds present in a sample and thereby to generate theselectivity for the measurement, this has severely limited the utilityof electrochemical methods for the analysis of many complex matrices. Incontrast, sinusoidal voltammetry can exploit the vast diversity inelectron transfer rates observable at solid electrodes (k⁰, the rate ofelectron transfer) can vary over ten orders of magnitude at the sameelectrode surface) to obtain additional selectivity in theelectrochemical measurement.

The composition of the frequency spectrum is extremely dependent on therate of electron transfer. By adjusting the frequency of the sinusoidal(or other time-varying) excitation waveform, it becomes possible to usethis kinetic information as well as the phase information todiscriminate between two molecules which have very similarelectrochemical properties. For example, this technique has been usedfor the detection of the direct oxidation of double-stranded DNA atcopper electrodes (Singhal and Kuhr (1997) Anal. Chem., 69: 1662-1668).Where this is usually undetectable at conventional electrodes withstandard voltammetric techniques, the use of sinusoidal voltammetryallowed the measurement of 1.0 nM double-stranded DNA. The concentrationdetection limit (S/N=3) for this size of dsDNA at the 6th harmonic is3.2 pM. When coupled with a low-volume system, such as a monolayer ofthe adsorbed material, this allows detection of sub-zeptomole (10⁻²¹mole) quantities of the storage medium molecule(s) on the surface.

This procedure may ultimately degrade the memory in the absence of arefresh mechanism. The level of degradation will depend on the totalnumber of molecules ultimately used to ensure acceptable faulttolerance. To avoid degradation problems, however, a refresh cycle (awrite cycle resetting the memory to the read value) can be insertedimmediately after each read cycle is complete.

B) Reading from a Dynamic Hole Storage Medium.

The same methods as described above for the static hole storage mediacan also be used to read dynamic hole storage media. However, thedynamic hole storage media were designed for and afford the uniquepossibility of interrogating a particular memory location viaexamination of the impedance of the working electrode. This readingscheme is possible because the impedance is modulated by the hole thathops between the two identical porphyrinic macrocycle units orthogonalto the surface of the electrode. The frequency of hole hopping isdifferent depending on which pair of redox-active subunits is in anodd-hole state (and whether they are in a three-hole or one-hole state).The value of the bit can be read via determination of that frequency.This is most easily accomplished by an impedance measurement (preferablya function of frequency).

The “hole-hopping” state of the porphyrin will determine the conductivestate of the molecular monolayer. Since the hole(s) rapidly hop betweenthe two metalloporphyrins in the odd-hole oxidation states at rateswhich vary from the 100's of KHz to 100's of MHz, depending on the typeof porphyrin, it is possible to find these states by the frequency atwhich the impedance of the nanostructure dips. In contrast, when each Mgor Zn porphyrin contains the same number of holes, no hopping can occur.The rate of hole hopping will determine the impedance characteristics ofeach state of each porphyrin nanostructure in the chip, and a decreasein the cell impedance would be expected at the hole-hopping frequencyfor each state of each porphyrin. While characterization of thesehole-hopping states requires the collection of the entire frequencyspectrum, the actual read cycle of the DHMU storage medium need onlymonitor a single frequency at a time. Impedance measurements usinglock-in based systems apply only one frequency at a time to theelectrode; any other frequencies are nearly totally suppressed by thelock-in amplifier. Thus, it is possible to monitor the frequencycharacteristic of hole-hopping level of each state and simultaneouslydetermine the logic level of each element in the array using lock-intechniques.

This method of reading is extremely sensitive for molecular memoriesthat utilize relatively small numbers of redox-active units (e.g.porphyrinic macrocycle nanostructures). The examination of the impedancecan also be performed without compromising the integrity of a particularmemory element.

For all I/O operations with the molecular memories of this invention,the use of molecular electronic components as on-chip buffering anddecoding circuitry is desirable although not required. Hybrid systemscan easily be produced incorporating the devices of this invention intoconventional integrated circuit packages that contain all the circuitryrequired for encoding/decoding data, reading and writing to the storageelement, monitoring fault tolerance and dynamically optimizing/selectingactive storage elements to maximize fault tolerance.

C) Instrumentation for Reading/Writing Molecular Memories.

As indicated above, the molecular memory devices can be read by any of awide variety of electrochemical technologies including amperometricmethods (e.g. chronoamperometry), coulometric methods (e.g.chronocoulometry), voltammetric methods (e.g., linear sweep voltammetry,cyclic voltammetry, pulse voltammetries, sinusoidal voltammetry, etc.),any of a variety of impedance and/or capacitance measurements, and thelike. Such readouts can be performed in the time and/or frequencydomain.

1) Fast Potentiostat/Voltammetry System.

In one preferred embodiment, readout is accomplished using a fastpotentiostat/voltammetry system. Such a system is capable of reading andwriting the memory elements, on a microsecond time scale. Such a systemcan be modified from a prototypical system described in U.S. Pat. No.5,650,061.

As illustrated in FIG. 11, a potentiostat with an RC time constant lessthan one microsecond is provided by using a fast voltage driver (e.g.,video buffer amplifier). A preferred video buffer amplifier retains ausable bandwidth beyond 20 MHz and is used to rephase the voltage andcurrent in the excitation signal to zero phase shift between voltage andcurrent. This rephasing of the excitation signal immediately before theworking electrode cancels out any phase shift which might be introducedby capacitance in the cable leading from the Arbitrary WaveformSynthesizer (AWS) function generator. An important part of the currentmonitor is a wide band op-amp. By using an op-amp with a very widegain-bandwidth product, the amplifier gain can be set to 10,000 andstill retain a bandwidth usable from DC to above 1 MHz. This allows thecollection of impedance data from electrodes as small as a 1 μm diskover a frequency range from 15 kHz to 5 MHz.

2) A Megahertz Impedance Analysis System.

An ultrafast impedance analysis system capable of characterizing theSHMU storage medium on a microsecond time scale can be constructed usingan Arbitrary Waveform Synthesizer (e.g., HP 8770A, AWS) and a 1-GHzDigitizing Oscilloscope (e.g., HP 54111D) controlled by a computersystem (e.g. HP 9000 series 300 computer system, Hewlett-Packard, PaloAlto, Calif.). The impedance data sets can be collected with the digitalscope with 8192 time domain points at 25 MHz. Thus, a full 8192 pointdata set can be acquired in a total of 328 μs. Both the excitation andthe response waveforms are measured; the excitation waveform is measuredprior to the start of the experiment so that the response acquisitionscan be done during the course of the experiment without interruption.One preferred excitation signal consists of a waveform with an amplitudeof 60 mV_((p-p)) which covers a frequency band from approximately 30 KHzto over 1 MHz. If five complete replicates of each excitation orresponse waveform are contained within the 8192 data points set capturedby the capture device (e.g. oscilloscope), because no further ensembleaveraging is needed, each full impedance spectra can be acquired in 328μs. Therefore, the whole frequency band under study can be excited andmonitored in a single acquisition. The FFT of the time domain dataprovides frequency-amplitude and frequency-phase characterization of thedata equivalent to the data given by a lock-in based system.

VIII. Computer Systems Comprising Storage Device(s) According to thisInvention.

The use of the storage devices of this invention in computer systems iscontemplated. One such computer system is illustrated in FIG. 12. Thecomputer comprises a signal source (e.g. I/O device or CPU) a storagedevice of this invention and appropriate circuitry (e.g. voltammetrycircuitry) to read the state(s) of the storage device. In operation,voltages representing the bits to be stored are applied to the workingelectrodes of the storage device thereby setting the memory. Whenretrieval is necessary (e.g. for output, or further processing) thestate(s) of the storage device is read by the I/O circuitry and theinformation is passed off to other elements (e.g. CPU) in the computer.

FIG. 12 illustrates the memory devices of this invention integrated intoa standard computer architecture or computer system 200. The hardware ofsystem 200 includes a processor (CPU) 205, a memory 206 (which cancomprise molecular memory devices), a persistent storage 208 which doescomprise molecular memory devices of this invention, and hardware for agraphical user interface (GUI) 220, coupled by a local bus or interface210. The persistent memory 208 can include the elements shown in FIG.11. System 200 can further include additional hardware components (notshown).

System 200 can be, for example, a personal computer or workstation.Processor 205 can be, for example, a microprocessor, such as the 80386,80486 or Pentium™ microprocessor, made by Intel Corp. (Santa Clara,Calif.). Memory 206 can include, for example, random-access memory(RAM), read-only memory (ROM), virtual memory, molecular memory (FIG.11) or any other working storage medium or media accessible by processor205. Persistent storage 208 can include a hard disk, a floppy disk, anoptical or magneto-optical disk, a molecular memory or any otherpersistent storage medium. GUI 220 facilitates communications between auser and system 200. Its hardware includes a visual display 221 and aselector device (mouse, keyboard, etc.) 222. Through visual display 221,system 200 can deliver graphical and textual output to the user. Fromselector device 222, system 200 can receive inputs indicating the user'sselection of particular windows, menus, and menu items. Visual display221 can include, for example, a cathode-ray tube (CRT) or flat-paneldisplay screen, or a head-mounted display such as a virtual realitydisplay. Selector device 222 can be, for example, a two-dimensionalpointing device such as a mouse, a trackball, a track pad, a stylus, ajoystick, or the like. Alternatively or additionally, selector device222 can include a keyboard, such as an alphanumeric keyboard withfunction and cursor-control keys.

The software of system 200 includes an operating system 250 and anapplication program 260. The software of system 200 can further includeadditional application programs (not shown). Operating system 150 canbe, for example, the Microsoft® Windows95® operating system for IBM PCand compatible computers having or emulating Intel 80386, 80486, orPentium™ processors. Alternatively, the operating system can bespecialized for operation utilizing molecular memory elements.Application program 160 is any application compatible with the operatingsystem and system 200 architecture. Persons of skill in the art willappreciate that a wide range of hardware and software configurations cansupport the system and method of the present invention in variousspecific embodiments.

EXAMPLES

The following examples are offered to illustrate, but not to limit theclaimed invention.

Example 1 Thiol-Porphyrins for Attachment to Electroactive Surfaces asMolecular Memory Devices

I. Molecular Design.

This example presents the design and synthesis of porphyrins that can beattached covalently, in defined geometries, to electroactive surfaces.For the present purposes, we consider only the surface of a goldelectrode. Three design features we sought to obtain included thefollowing: (1) The ability to attach porphyrins via a sulfide linkage tothe gold electrode surface with the porphyrins oriented vertically orhorizontally. (2) The ability to tune the porphyrin electrochemicaloxidation potential through the use of electron-withdrawing or releasingsubstituents at the periphery of the porphyrin, or the use of differentmetals in metalloporphyrins. (3) The use of thiol protecting groups thatwould cleave spontaneously on the gold surface, thereby avoiding thepotential practical problems of handling free thiols.

In order to achieve a vertical orientation of the porphyrin attached tothe gold surface, we employed A₃B meso-substituted porphyrins where theB group bears the thiol for surface attachment. The remaining three Agroups bear substituents for control of the electrochemical potential.In order to achieve a horizontal orientation of the porphyrin attachedto the gold surface, we employed porphyrins possessing two or four—CH₂SH groups in the meta position of the meso-phenyl rings. The tuningof the electrochemical potential can be achieved in a straightforwardmanner in the A₃B-porphyrins, where the A group can range fromelectron-rich substituents such as mesityl to electron-deficientsubstituents such as the pentafluorophenyl group. With thehorizontally-oriented porphyrins, the introduction of substituents totune the potential must be done without interfering with the meta-CH₂SHgroups. Accordingly, we have elected to investigate different metalswith the horizontally-positioned porphyrins. The selection of the thiolprotecting group poses extensive challenges. The protecting group ofchoice should be stable under diverse conditions, including the acidicand oxidative conditions of porphyrin formation as well as conditionsfor porphyrin metalation (generally involving mild Lewis acids, in somecases in the presence of bases). One objective is to be able toconstruct diarylethyne-linked multiporphyrin arrays, which requirePd-mediated coupling reactions. We sought thiol protecting groups thatwould meet these diverse criteria.

II. Results

Aldehydes

Our initial synthetic strategy toward mono-thiol (A₃B) porphyrins forvertical orientation started from 4-methylthiobenzaldehyde which wehoped to convert to 4-mercaptobenzaldehyde dimethyl acetal (using thestrategy of Young et al. (Young et al. (1984) Tetrahedron Lett., 25:1753-1756)) and next to the thiol-protected dimethyl acetals. The firststep involved conversion of the aldehyde group to its dimethyl acetalunder standard conditions. The sulfide obtained was successfullyconverted to the sulfoxide in 95% yield but treatment of the sulfoxidewith TFAA led to polymerization rather than the thiol (probably becauseof cleavage of acetal and intermolecular thioacetalization). We overcamethis problem by making two improvements: (1) the dimethyl acetal wasreplaced by a more bulky acetal protecting group at an earlier stage ofthe synthesis, (2) milder conditions for the Pummerer rearrangement wereemployed (Sugihara et al. (1978) Synthesis, 881). Thus protection of thecarbonyl group with neopentyl glycol (Rondestvedt (1961) J. Org. Chem.,26: 2247-2253) followed by oxidation of the resulting acetal (1)smoothly afforded sulfoxide 2 in 86% overall yield (Scheme 1, FIG. 14).Treatment of sulfoxide 2 with TFAA in the presence of 2,6-lutidinefollowed by hydrolysis of the resulting intermediate furnished thiol 3.Compound 3 was transformed into the S-protected acetals 4, 5, 6, and 7using ethyl isocyanoacetate (Ricci et al. (1977) J. Chem. Soc. PerkinTrans. 1: 1069-1073), 2,4-dinitrofluorobenzene (Vorozhtsov et al. (1958)Z. Obs. Chim., 28: 40-44, Engl. Transl. 40-44), 9-chloromethylanthracene(Kornblum and Scott (1974) J. Am. Chem. Soc., 96: 590-591), and pivaloylchloride, respectively, in overall yields of 20-65% from the sulfoxide2. The acetal group in 4, 5, 6 and 7 was selectively hydrolyzed prior toformation of the corresponding porphyrin.

Two other S-protected p-thiobenzaldehydes were obtained as shown inScheme 2 (FIG. 15). The thiocyanato-benzaldehyde 8 was preparedaccording to a general procedure (Suzuki and Abe (1996) Synth. Commun.,26: 3413-3419) in 20% yield. All attempts to improve the yield byreplacement of DMF with 1,3-dimethyl-2-imidazolidinone, increasing thetemperature, or prolonging the reaction time were unsuccessful.S-Acetylthiobenzaldehyde 9 was prepared in a two-step one-flaskprocedure. Cleavage of the methyl group of 4-methylthiobenzaldehydeaccording to a general procedure (Tiecco et al. (1982) Synthesis,478-480) followed by trapping of the resulting anion with acetylchloride afforded the desired S-acetylthiobenzaldehyde 9 in 55% yield.

Our approach toward horizontally-oriented porphyrins required access toS-protected m-(HSCH₂)benzaldehydes. The commercially availablem-(bromomethyl)benzonitrile was reduced with DiBAl—H to thecorresponding m-(bromomethyl)benzaldehyde (Wagner et al. (1997)Tetrahedron, 53: 6755-6790) (Scheme 2, FIG. 15). Substitution of thebromine with potassium thiocyanate gave the thiocyanato-benzaldehyde 10as colorless crystals in 74% yield. By using the thiocyanate asprotecting group, incorporation and protection of the sulfur unit couldbe achieved in one step.

Porphyrins

The A₃B-porphyrins were prepared using a two-step, one-flask roomtemperature synthesis of meso-substituted porphyrins that is compatiblewith a variety of precursor aldehydes including the ortho-disubstitutedbenzaldehydes that yield facially-encumbered porphyrins (Lindsey andWagner (1989) J. Org. Chem., 54: 828-836, Lindsey, J. S. inMetalloporphyrins-Catalyzed Oxidations; Montanari, F., Casella, L.,Eds.; Kluwer Academic Publishers: The Netherlands, 1994; pp 49-86,Lindsey et al. (1994) J. Org. Chem., 59: 579-587). A mixed-aldehydecondensation of mesitaldehyde, a thiol-protected aldehyde, and pyrroleafforded a mixture of porphyrins, from which the desired thiol-protectedA₃B-porphyrin was obtained by chromatography. The acetals 4-7 werehydrolyzed with trifluoroacetic acid and the resulting aldehydes 11-14were used directly without purification in the respective porphyrinsyntheses. Thus, aldehydes 9, 11, 12, 13 or 14 as well as commerciallyavailable 4-methylthiobenzaldehyde afforded thiol-protectedA₃B-porphyrins 20, 15, 16, 17, 18 or 19, respectively, in ˜10% yield(Scheme 3, FIG. 16). The porphyrins obtained were metalated usingZn(OAc)₂.2H₂O, affording Zn-20, Zn-15, Zn-16, Zn-17, Zn-18 or Zn-19.

Examination of the behavior of various thiol-protected zinc porphyrinsrevealed that the S—(N-ethylcarbamoyl) and S-acetyl groups easilycleaved in situ and the resulting porphyrin product bound on the goldsurface (vide infra). We decided to confirm this result by also cleavingthe S—(N-ethylcarbamoyl) group in porphyrin Zn-15 using basicconditions. Treatment of porphyrin Zn-15 with sodium methoxide followedby acidic workup gave mono-thiol porphyrin Zn-21, which wasair-sensitive and proved very difficult to purify to homogeneity (theporphyrin disulfide was also present) (Scheme 4, FIG. 17). The samereaction performed with quenching by acetyl chloride afforded theS-acetyl porphyrin Zn-20. Both Zn-15 and Zn-20 were found to bind to thegold surface identically with that of the free thiol containingporphyrin Zn-21.

We attempted to insert magnesium into porphyrins 15 and 16 using MgI₂and N,N-diisopropylethylamine in CH₂Cl₂ (Lindsey and Woodford (1995)Inorg. Chem. 34: 1063-1069). In both cases we obtained complex mixturesof porphyrins due to cleavage of the protecting groups. The resultingsalts likely contain the thiolate anion complexed with the protonateddiisopropylethylamine. All attempts at acidification caused demetalationof magnesium. Magnesium insertion occurred with5,10,15-trimesityl-20-(4-thiocyanatophenyl)porphyrin under theseconditions but the Mg-chelate could not be purified to homogeneity. Thedifficulty in purification may stem from lability of the thiocyanategroup on alumina, as we observed that the thiocyanate group of5,10,15-trimesityl-20-(4-thiocyanatophenyl)porphyrin is cleaved duringchromatography on alumina. Finally we subjected the S-acetyl-derivatizedporphyrin 20 to the same magnesium insertion conditions. Magnesiuminsertion occurred but with cleavage of the thiol protecting group,affording the free thiol Mg-21 in 32% yield (Scheme 5, FIG. 18).

The results of the gold-binding studies (vide infra) prompted us to usethe S-carbamoyl benzaldehyde 11 in subsequent syntheses. Thus mixedaldehyde-pyrrole condensations of aldehyde 11 with2,4,6-trimethoxybenzaldehyde, pentafluorobenzaldehyde, or n-hexanalyielded porphyrins 22, 23 or 24, respectively (Scheme 6, FIG. 19).Attempted conversion to the zinc chelate gave the thiol-protectedporphyrin Zn-22, however the more forcing conditions required formetalation of the tris(pentafluorophenyl)porphyrin andtri-n-pentyl-substituted porphyrin resulted in cleavage of theS—(N-ethylcarbamoyl) group, giving Zn-25 and Zn-26.

The design of porphyrins oriented in a horizontal manner can be achievedby the synthesis of porphyrins bearing a meta-(mercaptomethyl)phenylgroup at each of the four meso-positions. We attempted to repeat thesynthesis of the unprotected5,10,15,20-tetrakis[m-(mercaptomethyl)phenyl]porphyrin (Wen et al.(1997) J. Am. Chem. Soc., 119: 7726-7733), but encountered solubilityproblems due to disulfide formation. Because of the promising resultswith other thiol protecting groups cleaved directly on the gold surfacewe decided to synthesize the corresponding thiol-protected porphyrin. Asa protected sulfide entity we chose the thiocyanate group due to itshigh chemical stability.

Condensation of 10 with pyrrole at room temperature afforded the desired5,10,15,20-tetrakis[m-(thiocyanatomethyl)phenyl]porphyrin 27 as a darkpurple solid. Metalation with zinc acetate afforded the zinc-chelateZn-27 as a purple solid in 79% yield (Scheme 7, FIG. 20). Thethiocyanates were easily cleaved on the gold surface, affording aself-assembled porphyrin oriented parallel to the gold surface using allfour thiol groups for binding (vide infra).

Driven by these positive results we decided to synthesize a porphyrinwith only two ‘legs’ for attachment to the gold surface. Condensation ofaldehyde 10 with 5-phenyldipyrromethane (Lee and Lindsey (1994)Tetrahedron, 50: 11427-11440, Littler et al. (1999) J. Org. Chem., 64:1391-1396) using BF₃.OEt₂ in acetonitrile to minimize scrambling(Littler et al. (1999) J. Org. Chem., 64: 2864-2872) gave the desiredtrans-porphyrin 28 in 7% yield (accompanied by10,15,20-triphenyl-5-[m-(thiocyanatomethyl)phenyl]porphyrin in 2% yielddue to scrambling) (Scheme 8, FIG. 21). Metalation of 28 with zincacetate afforded the zinc porphyrin Zn-28 as a purple solid in 59%yield. Porphyrin Zn-28 also bound to the gold surface by in situcleavage of the thiocyanate units.

To achieve horizontally-oriented porphyrins with different potentials wedecided to metalate5,10,15,20-tetrakis[m-(S-acetylthiomethyl)phenyl]porphyrin (29) withvarious metal acetates (Scheme 9, FIG. 22). 29 was synthesized bysubstitution of all four bromides in5,10,15,20-tetrakis[m-(bromomethyl)phenyl)porphyrin (Wen et al. (1997)J. Am. Chem. Soc., 119: 7726-7733, Karaman et al. (1992) J. Am. Chem.Soc., 114: 4889-4898) with potassium thioacetate in 63% yield.Metalation of free base porphyrin 29 with zinc acetate gave the desiredzinc porphyrin Zn-29 in quantitative yield as a purple solid. UsingCo(OAc)₂.4H₂O afforded the corresponding cobalt chelate Co-29 as anorange-purple solid in quantitative yield.

Characterization

The synthetic porphyrins are purple solids with a metallic reflection.The porphyrins are stable to air but slowly decompose in solution in thepresence of light. The purity of all porphyrin compounds was routinelychecked by TLC, ¹H NMR spectroscopy (with the exception of theparamagnetic Co-29), LD-MS and UV/VIS spectroscopy. Fluorescenceemission and excitation spectroscopy was used to confirm thecompleteness of the different metalation procedures. FAB-MS and IRspectra were measured to support the structure of the porphyrins.

Generally the LD-MS spectrum of a porphyrin shows the cationic moleculeion peak M⁺ in high intensity with only little fragmentation (Srinivasanet al. (1999) J. Porphyrins Phthalocyanines, 3: 283-291). But someporphyrins with delicate peripheral groups undergo characteristic andextensive fragmentation upon I-D-MS analysis. Porphyrins withthiocyanate substituents show the loss of the cyano and the thiocyanatogroups, with the latter exhibiting more intense peaks. If more than onethiocyanate group is present, fragmentation can occur for each of thesegroups. Porphyrins with S-acetyl groups show loss of both the acetyl(—COCH₃) and the thioacetate (—SCOCH₃) groups. Such fragmentation cangenerally occur for each thioacetate substituent. A further LD-MSfeature observed with thioacetate-derivatized porphyrins involves theappearance of an (M+15)⁺ peak. Because this peak occurred in the LD-MSspectra of all porphyrins with thioacetate substituents, which weresynthesized via different routes, and no other types of spectra show anyevidence for the presence of another species, this cannot be an impuritybut must be a photochemical artifact involving the transfer of a methylgroup. In each case the (M+15)⁺ peak exhibited the same pattern offragmentation as observed for the parent molecule ion (M)⁺. Theintensity of the (M+15)⁺ peak is about 10% of that of the M⁺ peak.

Behavior on Gold

We surveyed the behavior of the thiol-protected zinc chelates Zn-15,Zn-16, Zn-17, Zn-18, Zn-19 and Zn-20 on gold electrodes. The members ofthis set of zinc porphyrins each bears three mesityl groups and differonly in the nature of the thiol protecting group. These studies revealedthat the S—(N-ethylcarbamoyl) (Zn-15) and S-acetyl (Zn-20) groups wereeasily cleaved on the gold surface, whereas the S-(2,4-dinitrophenyl)(Zn-16), S-(9-anthrylmethyl) (Zn-17), S-pivaloyl (Zn-18) and S-methyl(Zn-19) protecting groups were not cleaved. When no cleavage occurred,the thiol-protected porphyrins were not bound to the gold surface. Wefound that Zn-15 (S—(N-ethylcarbamoyl) protected), Zn-20 (S-acetylprotected), and Zn-21 (free thiol) bind to the gold surface identically.We also examined thiocyanatomethyl-derivatized porphyrins (Zn-27, Zn-28)on gold electrodes. We found that the thiocyanato protecting groupcleaves in situ and the corresponding thiol-derivatized porphyrin bindson the gold surface. These results are in accord with and extend aprevious report (Tour et al. (1995) J. Am. Chem. Soc. 117: 9529-9534)that the S-acetyl group of various thiol-substituted arenes (notporphyrins) is cleaved on the gold surface. Of the three thiolprotecting groups that we identified to undergo cleavage in situ on goldelectrodes, we also found in survey experiments that only the S-acetylgroup is compatible with Pd-coupling reactions for the preparation ofdiarylethyne-linked multiporphyrin arrays.

Porphyrins Zn-15, Zn-20, Zn-21, Zn-22, Zn-25, Zn-26, Zn-27, Zn-28, andMg-21 have been attached to a gold electrode. Porphyrins Zn-15, Zn-20,Zn-21, Zn-22, Zn-25, Zn-26, and Mg-21 bear one thiol or protected thioland bind to the gold surface in a vertical orientation. Porphyrins Zn-27and Zn-28 bind to the surface in a horizontal orientation with four andtwo sites of attachment, respectively. The set of zinc porphyrins withthree mesityl (Zn-15, Zn-20, Zn-21), n-pentyl (Zn-26),2,4,6-trimethoxyphenyl (Zn-22), or pentafluorophenyl (Zn-25) groups, aswell as the magnesium porphyrin with three mesityl groups (Mg-21),demonstrate the storage of data (upon oxidation) at differentelectrochemical potentials.

III. Experimental

General

All chemicals were obtained commercially and used as received unlessotherwise noted. Reagent grade solvents (CH₂Cl₂, CHCl₃, hexanes) andHPLC grade solvents (acetonitrile, toluene) were used as received fromFisher. Pyrrole was distilled from CaH₂. ¹H NM spectra (300 MHz, GeneralElectric GN 300NB), absorption spectra (HP 8453, Cary 3), and emissionspectra (Spex FluoroMax) were collected routinely. All reported NMRresults were obtained at 300 MHz in CDCl₃. UV-Vis absorption spectrawere recorded in CH₂Cl₂ or toluene. Flash chromatography was performedon flash silica (Baker, 200-400 mesh) or alumina (Fisher, 80-200 mesh).Mass spectra were obtained via laser desorption (LD-MS) in the absenceof an added matrix (Fenyo et al. (1997) J. Porphyrins Phthalocyanines,1: 93-99) using a Bruker Proflex II mass spectrometer, fast atombombardment (FAB-MS) using a JEOL HX110HF mass spectrometer (ion source40° C., CsKI or polyethylene glycol standards, 10 ppm elementalcompositional accuracy for the porphyrins), or electron-impact massspectrometry (EI-MS).

2-[(4-Methylthio)phenyl]-5,5-dimethyl-1,3-dioxane (1)

Samples of 4-methylthiobenzaldehyde (20.0 mL, 150 mmol), neopentylglycol (16.0 g, 155 mmol), toluene (250 mL) and p-toluenesulfonic acid(190 mg, 1.00 mmol) were placed in a 500 mL flask fitted with aDean-Stark trap and a reflux condenser. The mixture was refluxedcautiously until a sudden exotherm ceased, then for an additional hour(total ˜1.5 h). The cooled mixture was washed with sodium bicarbonatesolution and with water. After drying with Na₂SO₄ and evaporation, whitecrystals crystallized from hexanes (32.2 g, 89.4%). mp 74-75° C.; ¹H NMR(CDCl₃) δ 0.83 (s, 3H, CH₃C), 1.33 (s, 3H, CH₃C), 2.50 (s, 3H, CH₃S),3.67 (AB/2, 2H, CH₂O, J=10.2 Hz), 3.79 (AB/2, 2H, CH₂O, J=10.2 Hz), 5.25(s, 1H, acetal), 7.30, (AA′BB′, 4H, ArH); ¹³C NMR (CDCl₃) δ 16.5, 22.6,23.8, 30.9, 78.3, 102.1, 127.1, 127.4, 136.2, 140.0; EI-MS m/z 238.1028(M)⁺ (C₁₃H₁₈O₂S requires 238.1028); Anal. Calcd. for C₁₃H₁₈O₂S: C,65.51; H, 7.61; S, 13.45. Found: C, 65.62; H, 7.70; S, 13.55.

2-[(4-Methylsulfoxy)phenyl]-5,5-dimethyl-1,3-dioxane (2)

A solution of acetal 1 (19 g, 80 mmol) in CH₂Cl₂ (150 mL) was cooled to−20° C. and stirred vigorously. Then a solution of MCPBA (31 g of 50-55%water suspension, 90 mmol) in CH₂Cl₂ (100 mL) was added dropwise over 1h. The mixture was stirred at 0° C. for an additional 1 h. Then Ca(OH)₂(11 g, 0.15 mmol) and Na₂SO₄ (20 g) were added and stirring wascontinued for 1 h. After filtration and evaporation, the warm colorlessoil was dissolved in CH₂Cl₂ (20 mL) and hexanes was added, affordingwhite crystals that were isolated by filtration (14.6 g). The filtratewas evaporated and the residual oil was recrystallized, affording asecond crop of white crystals. The total yield was 19.6 g (97%). mp116-117° C.; ¹H NMR (CDCl₃) δ 0.77 (s, 3H, CH₃C), 1.24 (s, 3H, CH₃C),2.65 (s, 3H, CH₃SO), 3.62 (AB/2, 2H, CH₂O, J=11.1 Hz), 3.74 (AB/2, 2H,CH₂O, J=10.8 Hz), 5.40 (s, 1H, acetal), 7.6-7.7 (m, 4H, ArH); ¹³C NMR(CDCl₃) δ 22.5, 23.7, 30.9, 44.7, 78.3, 101.3, 124.0, 128.0, 142.2,146.7; EI-MS obsd 254.0975, calcd exact mass 254.0977 (C₁₃H₁₈O₃S); Anal.Calcd. for C₁₃H₁₈O₃S: C, 61.39; H, 7.13; S, 12.61. Found: C, 61.29; H,7.03; S, 12.70.

2-(4-Mercaptophenyl)-5,5-dimethyl-1,3-dioxane (3)

Sulfoxide 2 (7.62 g, 30.0 mmol) was dissolved in CH₃CN (120 mL).2,6-Lutidine (10.8 mL, 93.0 mmol) was added and the mixture was cooledto −20° C. To the resulting suspension TFAA (12.7 mL, 90.0 mmol) wasadded dropwise maintaining the temperature below 0° C. The sulfoxidedisappeared and the mixture turned a lemon yellow. When the addition wascomplete, the mixture was stirred at ˜0° C. for 1 h. The mixture wasthen allowed to warm to room temperature. All volatile materials wereevaporated at 30° C. Next a precooled mixture of NEt₃ (50 mL) and MeOH(50 mL) was added. After 30 min at room temperature all volatilematerials were evaporated under reduced pressure at low temperature. Theresidual yellow oil was dissolved in ether (70 mL) and extracted withsat. NH₄Cl (250 mL). The layers were separated, the organic layer wasdried (Na₂SO₄) and concentrated to dryness giving a yellow-orange oil(6.61 g, 98% yield of crude material) of which ˜70% was the desiredcompound. The crude thiol was pure enough for the next step. A smallsample was oxidized to the respective disulfide and characterized. mp134-136° C.; ¹H NMR (CDCl₃) δ 0.80 (s, 3H, CH₃C), 1.28 (s, 3H, CH₃C),3.63 (AB/2, 2H, CH₂O, J=10.2 Hz), 3.76 (AB/2, 2H, CH₂O, J=11.2 Hz), 5.36(s, 1H, acetal), 7.43, 7.49 (AA′BB′, 4H, ArH); ¹³C NMR (CDCl₃) δ 16.5,22.6, 23.7, 30.9, 78.3, 101.8, 127.6, 128.1, 138.2, 138.4; FAB-MS obsd446.1574, calcd exact mass 446.1586 (C₂₄H₃₀O₄S₂); Anal. Calcd. forC₂₄H₃₀O₄S₂, C, 64.54; H, 6.77; S, 14.36. Found: C, 64.52; H, 6.70; S,14.44.

2-[(4-S—(N-Ethylcarbamoyl)thiophenyl]-5,5-dimethyl-1,3-dioxane (4)

To the crude thiol 3 (6.60 g, 29.5 mmol) was added ethyl isocyanoacetate(2.33 mL, 29.5 mmol) followed by phenylthiotrimethylsilane (0.568 mL,3.00 mmol). The reaction mixture was stirred for 3 h at roomtemperature. During this time the mixture gradually solidified to a paleyellow solid. Then n-pentane (5 mL) was added and the suspension wasfiltered and washed thoroughly with n-pentane. The yellowish crystalswere dissolved in hot toluene and hexanes was added. After standing fora few hours, off-white crystals were collected (4.01 g, yield 45.2% fromsulfoxide 2). mp 117-118° C.; ¹H NMR (CDCl₃) δ 0.81 (s, 3H, CH₃C), 1.08(t, 3H, CH₃ —CH₂, J=7.2 Hz), 1.29 (s, 3H, CH₃C), 3.2-3.3 (m, 2H, CH₂N),3.67 (AB/2, 2H, CH₂O, J=10.8 Hz), 3.78 (AB/2, 2H, CH₂O, J=11.1 Hz), 5.42(s, 1H, acetal), 5.57 (bs, 1H, NH), 7.58 (bs, 4H, ArH); ¹³C NMR (CDCl₃)δ 15.5, 22.6, 23.7, 30.9, 37.2, 78.3, 101.5, 128.1, 130.0, 136.0, 140.7,166.4; El-MS obsd 295.1235, calcd exact mass 295.1242 (C₁₅H₂₁NO₃S);Anal. Calcd. for C₁₅H₂₁NO₃S: C, 60.99; H, 7.17; N, 4.74; S, 10.86.Found: C, 61.16; H, 7.05; N, 4.70; S, 11.02.

2-[(4-S-(2,4-Dinitrophenyl)thiophenyl]-5,5-dimethyl-1,3-dioxane (5)

Crude thiol 3 (1.00 g, 4.46 mmol) was mixed with2,4-dinitrofluorobenzene (830 mg, 4.46 mmol). After heating to 35° C.,cesium fluoride (1.35 g, 8.92 mmol) was added. The yellow mixture wasstirred and heated at 45° C. for 1 h. Next toluene (10 mL) was added andthe hot suspension was filtered to remove insoluble materials. Thefiltrate was evaporated to dryness, giving an orange oil. The crudeproduct was chromatographed on silica (CH₂Cl₂/hexaness 1:2) affording ayellow oil, which finally was crystallized from hot ethanol, affordingyellow crystals (1.2 g, 63% from sulfoxide 2). mp 132-133° C.; ¹H NMR(CDCl₃) δ 0.77 (s, 3H, CH₃C), 1.24 (s, 3H, CH₃C), 3.63 (AB/2, 2H, CH₂O,J=10.8 Hz), 3.74 (AB/2, 2H, CH₂O, J=11.1 Hz), 5.40 (s, 1H, acetal), 6.93(d, 1H, ArH-5, J=8.7 Hz), 7.57 (AA′BB′, 4H, ArH), 8.00 (dd, 1H, ArH-6,J=8.7 Hz, J=2.1 Hz), 8.99 (d, 1H, ArH-3, J=2.1 Hz); ¹³C NMR (CDCl₃) δ22.4, 23.6, 30.9, 78.4, 101.2, 122.0, 127.5, 129.2, 129,6, 130.0, 136.4,142.2, 144.9, 148.8; EI-MS obsd 390.0873, calcd exact mass 390.0886(C₁₈H₁₈N₂O₆S); Anal. Calcd. for C₁₈H₁₈N₂O₆S: C, 55.38; H, 4.65; N, 7.18;S, 8.21. Found: C, 55.50; H, 4.64; N, 7.12; S, 8.30.

2-[(4-S-(9-Anthrylmethyl)thiophenyl]-5,5-dimethyl-1,3-dioxane (6)

Crude thiol 3 (1.15 g, 50.0 mmol) was dissolved in methanol (10 mL). Tothis solution was added a freshly prepared solution of sodium methoxide[from Na (117 mg, 50.0 mmol) and MeOH (50 mL)]. After 15 min the mixturewas evaporated to dryness and the orange solid was dried under vacuum.Then the solid was dissolved in anhydrous DMF (15 mL) at roomtemperature and a solution of 9-chloromethylanthracene (1.13 g, 50.0mmol) in DMF (10 mL) was added. The reaction mixture was stirred at roomtemperature for 72 h. The DMF was evaporated under reduced pressure, andthe resulting yellow oil was chromatographed on alumina(hexanes/CH₂Cl₂). The resulting yellow crystals were recrystallized fromCH₂Cl₂/hexanes to afford 1.17 g of the desired product (56.4%). mp158-159° C.; ¹H NMR (CDCl₃) δ 0.84 (s, 3H, CH₃C), 1.37 (s, 3H, CH₃C),3.69 (AB/2, 2H, CH₂O, J=10.8 Hz), 3.84 (AB/2, 2H, CH₂O, J=10.8 Hz), 5.01(s, 2H, CH₂S), 5.44 (s, 1H, acetal), 7.4-7.6 (m, 8H, anthracene), 8.01,8.26 (AA′BB′, 4H, ArH), 8.42 (s, 1H, anthracene); ¹³C NMR (CDCl₃) δ22.6, 23.8, 30.9, 32.7, 78.4, 102.0, 124.8, 125.8, 127.1, 127.6, 128.1,128.5, 129.7, 129.9, 130.8, 132,2, 137.5, 139.3; FAB-MS obsd 414.1653,calcd exact mass 414.1654 (C₂₇H₂₆O₂S); Anal. Calcd. for C₂₇H₂₆O₂S: C,78.22; H, 6.32; S, 7.73. Found: C, 78.05; H, 6.24; S, 7.63.

2-[(4-S-Pivaloylthiophenyl]-5,5-dimethyl-1,3-dioxane (7)

Crude thiol 3 (2.24 g, 10.0 mmol) was dissolved in CH₂Cl₂ (10 mL) andmethanol (10 mL) was added. To this solution was added a freshlyprepared solution of sodium methoxide [from Na (230 mg, 10.0 mmol) andMeOH (5 mL)]. After 30 min pivaloyl chloride (1.40 mL, 11.4 mmol) wasadded and the mixture was stirred for an additional 3 h at roomtemperature. After evaporation of all volatile components, the residualoil was chromatographed on silica, affording a mixture of less polarcompounds. The yellowish oil was further chromatographed usingcentrifugal preparative chromatography to afford a mixture of the titlecompound and the corresponding disulfide. The mixture was dissolved inCH₂Cl₂ and MeOH was added. Next CH₂Cl₂ was flushed out with argon. Thecrystals were filtered and dissolved in hot methanol and the mixture wascarefully cooled. After 30 min crystals of the title compound werecollected (502 mg, 16.0%). mp 115-116° C.; ¹H NMR (CDCl₃) δ 0.80 (s, 3H,CH₃C), 1.28 (s, 3H, CH₃C), 1.32 (s, 9H, C(CH₃)₃), 3.64 (AB/2, 2H, CH₂O,J=10.2 Hz), 3.77 (AB/2, 2H, CH₂O, J=10.2 Hz), 5.41 (s, 1H, acetal),7.40, 7.55 (AA′BB′, 4H, ArH); ¹³C NMR (CDCl₃) δ 22.6, 23.7, 28.1, 30.9,47.6, 78.3, 101.6, 127.5, 129.3, 135.4, 140.1; Anal. Calcd. forC₁₇H₂₄O₃S: C, 66.20; H, 7.84; S, 10.40. Found: C, 66.22; H, 7.92; S,10.60.

4-Thiocyanatobenzaldehyde (8)

Under an argon atmosphere, a mixture of 4-iodobenzaldehyde (232 mg, 1.00mmol), KSCN (95.0 mg, 1.00 mmol), CuSCN (120 mg, 1.00 mmol) and DMF (7.5mL) was heated with stirring in an oil bath maintained at 140° C. for 12h. After cooling, the mixture was diluted with toluene and water, andthen filtered through a Celite bed. The aqueous phase was extracted withtoluene, the organic fractions were combined and washed with water,dried and concentrated. The resulting dark oil was chromatographed onsilica gel using centrifugal preparative chromatography to obtainoff-white crystals (33 mg, 20%). mp 82-83° C.; ¹H NMR (CDCl₃) δ 7.63,7.92 (AA′BB′, 2H, ArH), 10.01 (s, 1H, CHO); ¹³C NMR (CDCl₃) δ 109.4,129.3, 131.6, 132.9, 191.3; EI-MS obsd 163.0092, calcd exact mass163.0092 (C₈H₅NOS); Anal. Calcd. for C₈H₅NOS: C, 58.88; H, 3.09; N,8.58; S, 19.65. Found: C, 58.85; H, 2.99; N, 8.61; S, 19.68.

4-S-Acetylthiobenzaldehyde (9)

4-Methylthiobenzaldehyde (4.45 mL, 0.033 mol) and sodium thiomethoxide(10 g, 0.13 mol) were suspended in HMPA (100 mL) and the reactionmixture was heating with stirring at 100° C. for 18 h. The resultingbrown suspension was cooled and acetyl chloride (10 ml) was added. After2 h the resulting suspension was poured into water and diethyl ether wasadded. The ethereal layer was extracted with water three times, driedand evaporated. Next chromatography was performed (silica,CH₂Cl₂/hexanes, 1:1). A yellow oil was collected containing the titlecompound with some impurities (3.33 g, crude yield 55.5%). This oil wasrecrystallized from ethanol giving off-white crystals (1.05 g, 18.3%).mp 44-45° C. (lit. 46° C., Zhdanov et al. (1970) Zh. Organ. Khim., 6:554-559, Engl. Transl. (1970), 6: 551-555); ¹H NMR (CDCl₃) δ 2.44 (s,3H, COCH₃), 7.56 (AA′BB′, 2H, ArH), 7.87 (AA′BB′, 2H, ArH), 10.00 (s,1H, CHO); ¹³C NMR (CDCl₃) δ 31.2, 130.6, 135.2, 136.1, 137.1, 192.1,192.9; Anal. Calcd. for C₉H₈O₂S: C, 59.98; H, 4.47; S, 17.79. Found: C,59.58; H, 4.52; S, 17.78.

m-(Thiocyanatomethyl)benzaldehyde (10)

To a solution of 300 mg of m-(bromomethyl)benzaldehyde (Wagner et al.(1997) Tetrahedron, 53: 6755-6790) (1.5 mmol) in 5 mL of methanol wasadded a solution of 321 mg of potassium thiocyanate (3.3 mmol) in 4 mLof methanol under stirring at ambient temperature. After a few minutes aprecipitate formed. The reaction was monitored by TLC and stopped byadding 20 mL of H₂O when no starting material was detectable. 30 mL ofether was added and the phases were separated. The aqueous phase waswashed twice with 20 mL of ether and the combined organic phases weredried (Na₂SO₄). Column chromatography over flash silica gel withether/hexanes (1:2) gave 198 mg (1.1 mmol, 74% yield) of a slightlyyellow oil which solidified upon standing at 0° C. Recrystallization(ether/hexanes) gave colorless crystals (mp 39° C.). IR (neat): {tildeover (v)}=3060 cm⁻¹ (m, arom. CH), 2996 (m, CH), 2832 (s, CH), 2751 (m,CH), 2149 (s, CN), 1695 (s, C═O), 1603 (s, arom. C═C), 1450 (m, arom.C═C), 1424 (m), 1394 (w), 1294 (w), 1145 (s), 1084 (w), 1006 (w), 960(w), 908 (w), 881 (w), 803 (s), 754 (w), 696 (s), 652 (s); ¹H NMR (300.5MHz, CDCl₃): δ=4.22 (s, 2H, CH₂), 7.55-7.69 (m, 2H, ArH), 7.86 -7.93 (m,ArH), 10.04 (s, 1H, CHO); ¹³C NMR (75.6 MHz, CDCl₃, APT): δ=32.7 (+,CH₂), 111.4 (+, CN), 129.6 (−, CH), 129.8 (−, CH), 130.1 (−, CH), 134.6(−, CH), 135.7 (+, C_(q)), 136.8 (+, C_(q)), 191.4 (−, CHO); GC-MS (EI)obsd 177 [M⁺], 149 [M⁺ —CO], 120, 119 [M⁺ —SCN], 91 [M⁺ —SCN-CO], 90,89, 77 [C₆H₅ ⁺], 65, 63; Anal. Calcd for C₉H₇NOS, C, 60.99; H, 3.98; N,7.90; S, 18.09. Found: C, 60.75; H, 4.05; N, 7.86; S, 18.19.

General Procedure for Synthesis of Porphyrins 15-18, 19-20 and 22-24

Acetal (4, 5, 6 or 7) (0.730 mmol) was dissolved in CH₂Cl₂ (1 mL) andtrifluoroacetic acid (2 mL) was added. The mixture was stirred at roomtemperature overnight. After evaporation of the reaction mixture todryness, the residue was redissolved in CHCl₃ (40 mL). Alternatively,aldehyde 9 or 4-methylthiobenzaldehyde (0.730 mmol) was added to CHCl₃(40 mL). Next samples of the other aldehyde (2.20 mmol), pyrrole (0.200mL, 2.92 mmol) and BF₃.OEt₂ (0.090 mL, 0.71 mmol) were added. Thereaction mixture was stirred at room temperature for 90 min. Then DDQ(500 mg, 2.20 mmol) was added and the reaction mixture was gentlyrefluxed for 1 h. After cooling, the reaction mixture was passed over ashort silica column (CH₂Cl₂) affording porphyrins usually free from darkpigments and quinone species. Further purification details are describedfor each case as follows.

5,10,15-Trimesityl-20-[4-S—(N-ethylcarbamoyl)thiophenyl]porphyrin (15)

The mixture of porphyrins was loaded onto a silica column (4×30 cm,toluene). The title porphyrin comprised the second purple band,affording 72 mg (12%). ¹H NMR (CDCl₃) δ −2.47 (s, 2H, NHpyrrole), 1.32(t, 3H, CH₃ —CH₂, J=7.2 Hz), 1.94 (s, 18H, ArCH₃), 2.69 (s, 9H, ArCH₃),3.4-3.6 (m, 2H, CH₂N), 5.65 (bs, 1H, NH), 7.35 (s, 6H, ArH), 8.00, 8.33(AA′BB′, 4H, ArH), 8.72 (s, 4H, β-pyrrole), 8.78 (d, 2H, β-pyrrole,J=4.2 Hz), 8.87 (d, 2H, β-pyrrole, J=4.2 Hz); LD-MS calcd av mass 844.1,obsd 844.6 [M⁺], 773.1 [M⁺ —CONHEt]; FAB-MS obsd 843.4019, calcd exactmass 843.3971 (C₅₆H₅₃N₅OS); λ_(abs) (CH₂Cl₂) 419, 515, 548, 591 nm.

5,10,15-Trimesityl-20-[4-S-(2,4-dinitrophenyl)thiophenyl]porphyrin (16)

The mixture of porphyrins was purified by preparative centrifugal TLC(silica, toluene/hexanes, 1:2). The title porphyrin comprised the secondpurple band, affording 70 mg (10%). ¹H NMR (CDCl₃) δ −2.44 (s, 2H,NHpyrrole), 1.95 (s, 18H, ArCH₃), 2.71 (s, 9H, ArCH₃), 7.30 (d, 1H, ArH,J=8.1 Hz), 7.37 (s, 6H, ArH), 7.60 (d, 1H, ArH, J=8.7 Hz), 8.00, 8.49(AA′BB′, 4H, ArH), 8.75 (s, 4H, β-pyrrole), 8.8-9.0 (m, 4H, β-pyrrole),9.30 (d, 1H, ArH, J=2.1 Hz); LD-MS calcd av mass 938.4, obsd 938.0;FAB-MS obsd 938.3632, calcd exact mass 938.3614 (C₅₉H₅₀N₆O₄S); λ_(abs)(CH₂Cl₂) 419, 515, 549 591, 646 nm.

5,10,15-Trimesityl-20-[4-S-(9-anthrylmethyl)thiophenyl]Porphyrin (17)

The mixture was chromatographed on an alumina column (toluene/hexanes,1:4). The resulting mixture of porphyrins was purified by preparativecentrifugal TLC (silica, toluene/hexanes, 1:3). The title porphyrincomprised the second purple band, affording 28 mg (4.0%). ¹H NMR (CDCl₃)δ −2.51 (s, 2H, NHpyrrole), 1.90 (s, 18H, ArCH₃), 2.66 (s, 9H, ArCH₃),5.43 (s, 2H, CH₂S), 7.1-7.8 (m, 5H, anthracene), 7.31 (s, 6H, ArH),7.79, 8.52 (AA′BB′, 4H, ArH), 8.0-8.2 (m, 4H, anthracene), 8.68 (s, 4H,β-pyrrole), 8.75 (d, 2H, β-pyrrole, J=4.5 Hz), 8.80 (d, 2H, β-pyrrole,J=4.5 Hz); LD-MS calcd av mass 962.5, obsd 964.0, 787.4 [M⁺ —C₁₄H₈],773.1 [M⁺ —C₁₅H₁₀]; FAB-MS obsd 962.4368, calcd exact mass 962.4382(C₆₈H₅₈N₄S); λ_(abs) (CH₂Cl₂) 420, 515, 549, 593, 648 nm.

5,10,15-Trimesityl-20-[4-S-pivaloyl-thiophenyl]porphyrin (18)

The mixture was chromatographed on a silica column (toluene/hexanes,1:1). The title porphyrin comprised the second purple band, affording 68mg (11%). ¹H NMR (CDCl₃) δ-2.49 (s, 2H, NH), 1.52 (s, 9H, C(CH₃)₃), 1.92(s, 18H, ArCH₃), 2.68 (s, 9H, ArCH₃), 7.35 (s, 6H, ArH), 7.83, 8.30(AA′BB′, 4H, ArH), 8.70 (s, 4H, β-pyrrole), 8.75 (d, 2H, β-pyrrole,J=5.4 Hz), 8.88 (d, 2H, β-pyrrole, J=5.4 Hz); LD-MS calcd av mass 856.4,obsd 858.6, 831.5 [M⁺ —C₂H₆], 774.2 [M⁺ —COC(CH₃)₃]; FAB-MS obsd856.4186, calcd exact mass 856.4175 (C₅₈H₅₆N₄OS); λ_(abs) (CH₂Cl₂) 419,515, 548, 591, 646 nm.

5,10,15-Trimesityl-20-[4-S-methylthiophenyl]porphyrin (19)

The mixture was chromatographed on a silica column (toluene/hexanes, 1:1). The resulting mixture was next chromatographed on silica column(toluene/hexanes, 1:4). The title porphyrin comprised the second purpleband, affording 57 mg (10%). ¹H NMR (CDCl₃) δ-2.49 (s, 2H, NH), 1.92 (s,18H, ArCH₃), 2.68 (s, 9H, ArCH₃), 2.79 (s, 3H, SCH₃), 7.33 (s, 6H, ArH),7.67, 8.18 (AA′BB′, 4H, ArH), 8.70 (s, 4H, β-pyrrole), 8.74 (d, 2H,β-pyrrole, J=5.1 Hz), 8.87 (d, 2H, β-pyrrole, J=5.1 Hz); LD-MS calcd avmass 786.4, obsd 786.9; FAB-MS obsd 786.3790, calcd exact mass 786.3756(C₅₄H₅₀N₄S); λ_(abs) (CH₂Cl₂) 420, 515, 550, 592, 648 nm.

5,10,15-Trimesityl-20-[4-S-acetylthiophenyl]porphyrin (20)

The mixture was chromatographed on a silica column (toluene/hexanes 1:1,then toluene). The title porphyrin comprised the second purple band,affording 62 mg (10.5%). ^(H 1)NMR (CDCl₃) δ-2.46 (s, 2H, NH), 1.94 (s,18H, ArCH₃), 2.66 (s, 3H, COCH₃), 2.70 (s, 9H, ArCH₃), 7.35 (s, 6H, ArH,7.88, 8.35 (AA′BB′, 4H, ArH), 8.73 (s, 4H, β-pyrrole), 8.79 (d, 2H,β-pyrrole, J=4.2 Hz), 8.89 (d, 2H, β-pyrrole, J=4.2 Hz); LD-MS calcd avmass 814.4, obsd 815.7, 813.9 [M⁺+15]; 787.7 [M⁺ —CH₃CO+15], 773.7[M⁺-CH₃CO]; FAB-MS obsd 814.3694, calcd exact mass 814.3705(C₅₅H₅₀N₄OS); λ_(abs) (CH₂Cl₂) 419, 515, 548, 591, 647 nm.

5,10,15-Tris(2,4,6-trimethoxyphenyl)-20-[4-S—(N-ethylcarbamoyl)thiophenyl]porphyrin(22)

Purification was performed by preparative centrifugal chromatography(silica, CH₂Cl₂/MeOH, 98:2). The title compound was obtained as a ˜1:1mixture with 5,10,15,20-tetrakis(2,4,6-trimethoxyphenyl)porphyrin. Thepresence of the title compound was confirmed by mass spectrometry (LD-MSC₅₆H₅₃N₅O₁₀S calcd av mass 987.4, obsd 988.6). This mixture was notpurified further but was used in the metalation reaction to prepareZn-22.

5,10,15-Tris(2,3,4,5,6-pentafluorophenyl)-20-[4-S—(N-ethylcarbamoyl)thiophenyl]-porphyrin(23)

The mixture of porphyrins was chromatographed on a silica column (4×30cm, hexanes/CH₂Cl₂, 2:1). The title porphyrin comprised the secondpurple band, affording 72 mg (10%). ¹H NMR (CDCl₃) δ-2.74 (s, 2H,NHpyrrole), 1.32 (t, 3H, CH₃ —CH₂, J=7.2 Hz), 3.5-3.6 (m, 2H, CH₂N),5.67 (bs, 1H, NH), 8.00, 8.32 (AA′BB′, 4H, ArH), 8.94 (d, 2H, β-pyrrole,J=5.1 Hz), 9.02 (s, 4H, β-pyrrole), 9.09 (d, 2H, β-pyrrole, J=4.2 Hz);LD-MS calcd av mass 987.1, obsd 989.9, 918.7 [M⁺ —CONHEt]; FAB-MS obsd987.1136, calcd exact mass 987.1149 (C₄₇H₂₀F₁₅N₅OS); λ_(abs) (CH₂C₁₂)415, 509, 540, 584, 638 nm.

5,10,15-Tri-n-pentyl-20-[4-S—(N-ethylcarbamoyl)thiophenyl]porphyrin (24)

The free base was purified by preparative centrifugal chromatography(silica/CH₂Cl₂/hexanes, 5:1) followed by column chromatography(silica/CH₂Cl₂/toluene, 4:1). The title porphyrin comprised the secondpurple band, affording 9 mg (4%). ¹H NMR (CDCl₃) δ-2.62 (s, 2H, NH),1.00-1.10 (m, 9H, CH₃ —CH₂), 1.30-1.70 (m, 9H, CH₂ aliphatic+CH₃—CH₂—N), 1.75-1.90 (m, 6H, CH₂), 2.45-2.70 (m, 6H, CH₂), 3.50-3.62 (m,4H, N—CH₂), 4.90-5.10 (m, 6H, CH₂-porphyrin), 5.63 (bt, 1H, NH,J=5.1Hz), 7.98, 8.26 (AA′BB′, 4H, ArH), 8.85 (d, 2H, β-pyrrole, J=4.2Hz), 9.43 (d, 2H, β-pyrrole, J=5.1 Hz); 9.52-9.62 (m, 4H, β-pyrrole);LD-MS calcd av mass 699.4, obsd 700.7; FAB-MS obsd 699.3996, calcd exactmass 699.3971 (C₄₄H₅₃N₅OS); λ_(abs) (CH₂Cl₂) 419, 519, 554, 598, 656 nm.

General Procedure for Zinc Insertion

Porphyrin (0.040 mmol) was dissolved in CH₂Cl₂ (15 mL) and a solution ofZn(OAc)₂.2H₂O (880 mg, 4.00 mmol) in methanol (15 mL) was added. Thereaction mixture was stirred overnight at room temperature. Aftermetalation was complete (TLC, fluorescence excitation spectroscopy), thereaction mixture was washed with water and 10% NaHCO₃, dried (Na₂SO₄),filtered and rotary evaporated to a purple solid. Purification wasachieved by chromatography on silica.

Zn(II)-5,10,15-Trimesityl-20-[4-S—(N-ethylcarbamoyl)thiophenyl]porphyrin(Zn-15)

Column chromatography (silica, CH₂Cl₂) afforded 29 mg (75%). ¹H NMR(CDCl₃) δ 1.30 (t, 3H, CH₃ —CH₂, J=7.5 Hz), 1.87 (s, 18H, ArCH₃), 2.66(s, 9H, ArCH₃), 3.4-3.6 (m, 2H, CH₂N), 5.61 (bs, 1H, NH), 7.31 (s, 6H,ArH), 7.93, 8.30 (AA′BB′, 4H, ArH), 8.74 (s, 4H, β-pyrrole), 8.80 (d,2H, β-pyrrole, J=5.1 Hz), 8.88 (d, 2H, β-pyrrole, J=4.2 Hz); LD-MS calcdav mass 905.3, obsd 906.7, 835.7 [M⁺ —CONHEt]; FAB-MS obsd 905.3098,calcd exact mass 905.3106 (C₅₆H₅₁N₅OSZn); λ_(abs) (CH₂Cl₂) 421, 549 nm.

Zn(II)-5,10,15-Trimesityl-20-[4-S-(2,4-dinitrophenyl)thiophenyl]porphyrin(Zn-16)

Column chromatography (silica, toluene/hexanes) afforded 34 mg (85%). ¹HNMR (CDCl₃) δ 1.87 (s, 18H, ArCH₃), 2.64 (s, 9H, ArCH₃), 7.26 (d, 1H,ArH, J=9.0 Hz), 7.29 (s, 6H, ArH), 7.54 (d, 1H, ArH, J=9.0 Hz), 7.99,8.44 (AA′BB′, 4H, ArH), 8.75 (s, 4H, β-pyrrole), 8.86 (AB, 4H,β-pyrrole, J=4.5 Hz), 9.23 (d, 1H, ArH, J=3.0 Hz); LD-MS calcd av mass1000.3, obsd 1000.3; FAB-MS obsd 1000.2726, calcd exact mass 1000.2749(C₅₉H₄₈N₆O₄SZn); λ_(abs) (CH₂Cl₂) 422, 550 nm.

Zn(II)-5,10,15-Trimesityl-20-[4-S-(9-anthrylmethyl)thiophenyl]porphyrin(Zn-17)

The product was purified by preparative centrifugal TLC (silica,hexanes/CH₂Cl₂) 31 mg (74%). ¹H NMR (CDCl₃) δ 1.85 (s, 9H, ArCH₃), 1.88(s, 9H, ArCH₃), 2.65 (s, 9H, ArCH₃), 5.36 (s, 2H, CH₂S), 7.1-8.5 (m,19H, anthracene+ArH), 8.72 (s, 2H, β-pyrrole), 8.73 (s, 2H, β-pyrrole),8.8-9.0 (m, 4H, β-pyrrole); LD-MS calcd av mass 1024.4, obsd 1027.3,834.9 [M⁺ —C₁₅H₁₀]; FAB-MS obsd 1024.3529, calcd exact mass 1024.3517(C₆₈H₅₆N₄SZn); λ_(abs) (CH₂Cl₂) 421, 550 nm.

Zn(II)-5,10,15-Trimesityl-20-[4-S-pivaloylthiophenyl]porphyrin (Zn-18)

The product was purified on a silica column (toluene/hexanes, 1:1),affording 31 mg (85%). ¹H NMR (CDCl₃) δ 1.50 (s, 9H, C(CH₃)₃), 1.87 (s,18H, ArCH₃), 2.65 (s, 9H, ArCH₃), 7.31 (s, 6H, ArH), 7.79, 8.29 (AA′BB′,4H, ArH), 8.74 (s, 4H, β-pyrrole), 8.79 (d, 2H, β-pyrrole, J=4.2 Hz),8.91 (d, 2H, β-pyrrole, J=4.2 Hz); LD-MS calcd av mass 918.3, obsd919.5, 891.4 [M⁺ —C₂H₆], 835.3 [M⁺ —COC(CH₃)₃]; FAB-MS obsd 918.3332,calcd exact mass 918.3310 (C₅₈H₅₄N₄OSZn); λ_(abs) (CH₂Cl₂) 422, 549 nm.

Zn(II)-5,10,15-Trimesityl-20-[4-S-methylthiophenyl]porphyrin (Zn-19)

The mixture was chromatographed on a silica column (toluene/hexanes,1:1). The resulting mixture was next chromatographed on a silica column(toluene/hexanes, 1:4). The title porphyrin comprised the second purpleband, affording 31 mg (90%). ¹H NMR (CDCl₃) δ 1.84 (s, 18H, ArCH₃), 2.63(s, 9H, ArCH₃), 2.74 (s, 3H, SCH₃), 7.26 (s, 6H, ArH), 7.59, 8.13(AA′BB′, 2H, ArH), 8.70 (s, 4H, β-pyrrole), 8.75 (d, 2H, β-pyrrole,J=5.1 Hz), 8.87 (d, 2H, β-pyrrole, J=5.1 Hz); LD-MS calcd av mass 848.3,obsd 851.5; FAB-MS obsd 848.2913, calcd exact mass 848.2891(C₅₄H₄₈N₄SZn); λ_(abs) (CH₂Cl₂) 421, 550 nm.

Zn(II)-5,10,15-Trimesityl-20-[4-S-acetylthiophenyl]porphyrin (Zn-20)

Method 1.

(From 20 by general zinc insertion procedure). Purification bychromatography (silica, toluene/CH₂Cl₂). Yield 82%.

Method 2.

Zn(II)-porphyrin Zn-15 (9.0 mg, 0.010 mmol) was dissolved in CH₂Cl₂ (20mL) and the solution was carefully flushed with argon. Next a solutionof sodium methoxide [freshly prepared from sodium (23 mg, 1.0 mmol) andMeOH (10 mL) under argon] was added. The reaction mixture was stirredunder argon at room temperature for 1 h. Next acetyl chloride (1 mmol,0.7 mL) was added and the mixture was evaporated to dryness. The mixtureof porphyrins was dissolved in CH₂Cl₂ and chromatographed (silica,hexanes/CH₂Cl₂) affording 6.3 mg (72%). ¹H NMR (CDCl₃) δ 1.85 (s, 18H,ArCH₃), 2.63 (s, 9H, ArCH₃), 2.61 (s, 3H, CH₃CO), 7.28 (s, 6H, ArH),7.46, 8.07 (AA′BB′, 4H, ArH), 8.70 (s, 4H, β-pyrrole), 8.74 (d, 2H,β-pyrrole, J=5.1 Hz), 8.83 (d, 2H, β-pyrrole, J=5.1 Hz); LD-MS calcd avmass 876.3, obsd 874.6; FAB-MS obsd 878.2983, calcd exact mass 878.2997(C₅₅H₅₀N₄OSZn).

Zn(II)-5,10,15-Trimesityl-20-[4-mercaptophenyl]porphyrin (Zn-21)

A sample of Zn-15 (9.0 mg, 0.010 mmol) was dissolved in CH₂Cl₂ (20 mL)and the solution was carefully flushed with argon. Next a solution ofsodium methoxide [freshly prepared from sodium (23 mg, 1 mmol) and MeOH(10 mL) and also flushed with argon] was added. The reaction mixture wasstirred at room temperature for 1 h. Next HCl (0.2 mL, 5 M soln.) wasadded and the mixture was evaporated to dryness. The mixture ofporphyrins was dissolved in CH₂Cl₂ and chromatographed (silica,hexanes/CH₂Cl₂) affording 4.3 mg (51%). ¹H NMR (CDCl₃) δ 1.89 (s, 18H,ArCH₃), 2.66 (s, 9H, ArCH₃), 7.31 (s, 6H, ArH), 7.64, 8.22 (AA′BB′, 2H,ArH), 8.76 (s, 4H, β-pyrrole), 8.8-9.0 (m, 4H, β-pyrrole); LD-MS calcdav mass 834.3, obsd 834.0; FAB-MS obsd 834.2071, calcd exact mass834.2735 (C₅₃H₄₆N₄SZn).

Zn(II)-5,10,15-Tris(2,4,6-trimethoxyphenyl)-20-[4-S—(N-ethylcarbamoyl)thiophenyl]-porphyrin(Zn-22)

30.0 mg of a mixture of the desired free base A₃B-porphyrin and thecorresponding A₄-porphyrin was metalated according to the generalprocedure. The desired chelate was purified by preparative centrifugalchromatography (silica/CH₂Cl₂/MeOH, 99:1), affording 10.0 mg (1.3% fromacetal 5). ¹H NMR (CDCl₃) δ 1.27 (t, 3H, CH₃ —CH₂, J=7.2 Hz), 3.4-3.6(m, 2H, CH₂N), 3.49 (s, 18H, OCH₃), 4.09 (s, 9H, OCH₃), 5.57 (bt, 1H,NH, J=5.1 Hz), 6.57 (s, 6H, ArH), 7.89, 8.26 (AA′BB′, 4H, ArH), 8.81 (d,2H, β-pyrrole, J=4.5 Hz), 8.86 (d, 2H, β-pyrrole, J=4.5 Hz), 8.84 (s,4H, β-pyrrole); LD-MS calcd av mass 1049.3, obsd 1052.7, 981.5 [M⁺—CONHEt]; FAB-MS obsd 1049.2666, calcd exact mass 1049.2648(C₅₆H₅₁N₅O₁₀SZn); λ_(abs) (CH₂Cl₂) 423, 549 nm

Zn(II)-5,10,15-Tris(2,3,4,5,6-pentafluorophenyl)-20-[4-mercaptophenyl]porphyrin(Zn-25)

Refluxing a mixture of porphyrin 25 and Zn(OAc)₂.2H₂O for 8 h followedby purification on silica (CH₂Cl₂) afforded 25 mg (63% yield). ¹H NMR(CDCl₃) δ 3.79 (s, 1H, SH), 7.67, 8.09 (AA′BB′, 4H, ArH), 8.93 (d, 2H,β-pyrrole, J=4.2 Hz), 9.00 (s, 4H, β-pyrrole), 9.09 (d, 2H, β-pyrrole,J=4.2 Hz); LD-MS calcd av mass 978.0, obsd 975.4; FAB-MS obsd 977.9925,calcd exact mass 977.9913 (C₄₄H₁₃F₁₅N₄SZn). λ_(abs) (CH₂Cl₂) 416, 545nm.

Zn(II)-5,10,15-Tri-n-pentyl-20-[4-mercaptophenyl]porphyrin (Zn-26)

The product was purified by column chromatography (silica/CH₂Cl₂)followed by preparative centrifugal TLC (silica, hexanes/CH₂Cl₂, 1:9),affording 12 mg (44%). ¹H NMR (CDCl₃) δ 0.80-1.40 (m, 12H, CH₃ —CH₂+CH₃—CH₂—N), 1.50-1.70 (m, 6H, CH₂ aliphatic), 1.75-1.95 (m, 6H, CH₂),2.40-2.60 (m, 6H, CH₂), 4.70-4.90 (m, 6H, CH₂-porphyrin), 8.17, 8.28(AB′BB′, 4H, ArH), 8.95 (d, 2H, β-pyrrole, J=5.1 Hz), 9.35-9.48 (d, 6H,β-pyrrole); LD-MS calcd av mass 690.3, obsd 690.4, 633.1 [M⁺ —C₄H₉];FAB-MS obsd 690.2706, calcd exact mass 690.2735 (C₄₁H₄₆N₄SZn); λ_(abs)(CH₂Cl₂) 419, 554 nm.

Mg(II)-5,10,15-Trimesityl-20-[4-mercaptophenyl]porphyrin (Mg-21)

Porphyrin 20 (16 mg, 0.020 mmol) was dissolved in CH₂Cl₂ (5 mL) and MgI₂(56 mg, 0.20 mmol) and DIEA (0.070 mL, 0.40 mmol) were added. After 10min the mixture was diluted with CH₂Cl₂ (20 mL), washed with 10% NaHCO₃and dried. The resulting pink-violet residue was chromatographed on analumina column (CH₂Cl₂/MeOH, 100:1, 100:2, 100:4) to afford thepink-violet product (5.0 mg, 31%). ¹H NMR (CDCl₃) δ 1.80 (s, 18H,ArCH₃), 2.61 (s, 9H, ArCH₃), 7.23 (s, 6H, ArH), 7.8-8.1 (m, 4, ArH),8.5-8.9 (m, 8H, β-pyrrole); LD-MS calcd av mass 795.3, obsd 797.4;FAB-MS obsd 794.3278, calcd exact mass 794.3294 (C₅₃H₄₆N₄SMg); λ_(abs)(CH₂Cl₂) 426, 565, 605 nm.

5,10,15,20-Tetrakis[m-(thiocyanatomethyl)phenyl]porphyrin (27)

A solution of 513 mg of m-(thiocyanatomethyl)benzaldehyde (10, 2.9 mmol)and 0.20 mL of pyrrole (193 mg, 2.9 mmol) in 300 mL of CHCl₃ was purgedwith argon for 30 min. Under stirring at ambient temperature 12 μL ofBF₃.O(Et)₂ (13 mg, 0.1 mmol) and 180 μL of TFA (266 mg, 2.3 mmol) wereadded. Soon the solution turned yellow and later to dark red. After 2 han additional 90 μL of BF₃.O(Et)₂ (98 mg, 0.7 mmol) was added. After 2 h500 μL of TEA (364 mg, 3.6 mmol) and 583 mg of o-tetrachlorobenzoquinone(2.4 mmol) were added and the mixture was refluxed for 1 h. The mixturewas cooled to room temperature and the solvents were removed underreduced pressure. Column chromatography over flash silica gel withether/hexanes (3:1) gave 119 mg (0.1 mmol, 18% yield) of a dark purplesolid. IR (neat) {tilde over (v)}=2953 (m, CH), 2917 (s, CH), 2846 (m,CH), 2152 (m, CN), 1470 (m), 1392 (w), 1344 (w), 1152 (w), 1082 (w); ¹HNMR (300.5 MHz, CDCl₃): δ=-2.84 (s, 2H, NH), 4.44 (s, 8H, CH₂),7.76-7.85 (m, 8H, ArH), 8.18-8.25 (m, 8H, ArH), 8.88 (s, 8H, β-pyrrole);LD-MS calcd av mass 899.1, obsd 901.7, 876.3 [M⁺-CN], 843.5 [M⁺ —SCN],818.1 [M⁺ —SCN—CN], 785.1 [M⁺-2SCN], 758.5 [M⁺-2SCN—CN], 726.8[M⁺-3SCN], 668.0 [M⁺-4SCN], 577.6 [M⁺-4SCN—C₇H₇]; FAB-MS obsd 898.1797,calcd exact mass 898.1789 (C₅₂H₃₄N₈S₄); λ_(abs) (toluene) 420, 514, 549,590, 646 nm.

Zinc(II)-5,10,15,20-Tetrakis[m-(thiocyanatomethyl)phenyl]porphyrin(Zn-27)

To a solution of 84 mg of5,10,15,20-tetrakis[m-(thiocyanatomethyl)phenyl]porphyrin (27, 93 μmol)in 50 mL of CHCl₃ was added 250 mg of Zn(OAc)₂.2H₂O (1.1 mmol) in 5 mLof methanol under stirring at ambient temperature. After completion ofthe metalation (checked by fluorescence excitation spectroscopy) themixture was washed with 20 mL of 10% NaHCO₃ and 20 mL of H₂O, dried(Na₂SO₄) and filtered. The solvents were removed under reduced pressureaffording 71 mg (74 μmol, 79% yield) of a dark purple solid.Recrystallization (CH₂Cl₂/methanol) gave dark purple crystals. IR(neat): {tilde over (v)}=2995 (m, CH), 2880 (w, CH), 2153 (m, CN), 1652(w), 1601 (m, arom. C═C), 1478 (m), 1436 (m), 1338 (m), 1206 (m), 1070(w), 1031 (w), 1001 (s), 934 (m), 795 (s), 707 (s); ¹H NMR (300.5 MHz,CDCl₃): δ=4.44 (s, 8H, CH₂), 7.77-7.83 (m, 8H, ArH), 8.20-8.25 (m, 8H,ArH), 8.97 (s, 8H, β-pyrrole); LD-MS calcd av mass 962.5, obsd 958.2,900.2 [M⁺ —SCN], 843.5 [M⁺-2SCN], 787.5 [M⁺-3SCN], 726.7 [M⁺-4SCN];FAB-MS obsd 960.0959, calcd exact mass 960.0924 (C₅₂H₃₂N₈S₄Zn); λ_(abs)(toluene) 422, 550, 589 nm; λ_(em) (toluene) 603, 652 nm.

10,20-Diphenyl-5,15-bis[-m-(thiocyanatomethyl)phenyl]porphyrin (28)

A mixture of 316 mg of m-(thiocyanatomethyl)benzaldehyde (10, 1.8 mmol),396 mg of 5-phenyldipyrromethane (Lee and Lindsey (1994) Tetrahedron,50: 11427-11440, Littler et al. (1999) J. Org. Chem., 64: 1391-1396)(1.8 mmol) and 1.07 g of NH₄Cl (20.0 mmol) in 200 mL of acetonitrile waspurged with argon for 30 min. Under stirring at ambient temperature 23μL of BF₃.O(Et)₂ (26 mg, 0.18 mmol) was added. Soon the solution turnedto yellow and later to dark red. After 6.5 h, 607 mg of DDQ (2.7 mmol)was added. After 1 h the reaction was quenched with 0.5 mL of TEA (365g, 3.6 mmol). The solvents were removed under reduced pressure.Purification was done by column chromatography over two flash silica gelcolumns with different solvent mixtures: (column 1) ether/hexanes (3:1)and (column 2) CH₂Cl₂/hexanes (gradient, start: 1:1). Two fractions ofdark purple solids were obtained. I: 12 mg10,15,20-triphenyl-5-[m-(thiocyanatomethyl)phenyl]porphyrin (17.5 μmol,2% yield). II: 44 mg of the title compound (58.1 μmol, 7% yield). IR(neat): {tilde over (v)}=2921 (s, CH), 2850 (m, CH), 2154 (m, CN), 1597(m, arom. C═C), 1471 (s), 1348 (m), 1206 (m), 1181 (w), 1097 (w), 973(s), 898 (w), 743 (s), 691 (s), 623 (s); ¹H NMR (300.5 MHz, CDCl₃):δ=-2.811 (s, 2H, NH), 4.57 (s, 4H, CH₂), 7.71-7.83 (m, 11H, ArH),8.17-8.25 (m, 8H, ArH), 8.84 (d, 4H, β-pyrrole, ³J=5.1 Hz), 8.88 (d, 4H,β-pyrrole); LD-MS calcd av mass 756.9, obsd 757.4, 699.2 [M⁺-SCN], 641.0[M⁺-2SCN]; FAB-MS obsd 756.2172, calcd exact mass 756.2130 (C₄₈H₃₂N₆S₂);λ_(abs) (toluene) 420, 514, 549, 590, 647, 657 nm.

Zinc(II)-10,20-Diphenyl-5,15-bis[-m-(thiocyanatomethyl)phenyl]porphyrin(Zn-28)

A mixture of 38 mg of10,20-diphenyl-5,15-bis[m-(thiocyanatomethyl)phenyl]porphyrin (28, 50.2μmol) in 30 mL of CH₂Cl₂ and a solution of 140 mg of Zn(OAc)₂.2H₂O (0.64mmol) in 5 mL of methanol were combined and stirred at ambienttemperature. After completion of the metalation (checked by fluorescenceexcitation spectroscopy) 20 mL of H₂O were added. The phases wereseparated and the organic layer was washed with 20 mL of 5% NaHCO₃ and20 mL of H₂O, dried (Na₂SO₄) and filtered. The solvents were removedunder reduced pressure. Column chromatography over flash silica gel withCH₂Cl₂/hexanes (5:1) gave 22 mg (26.8 μmol, 53% yield) of a dark purplesolid. IR (neat): {tilde over (v)}=3049 (w, arom. CH), 2924 (s, CH),2853 (m, CH), 2154 (m, CN), 1598 (m, arom. C═C), 1522 (w), 1480 (m),1440 (m), 1339 (m), 1206 (m), 1070 (m), 1002 (s), 934 (w), 796 (s), 741(m), 703 (s), 662 (m); ¹H NMR (300.5 MHz, CDCl₃): δ=4.44 (s, 4H, CH₂),7.70-7.90 (m, 11H, ArH), 8.16-8.28 (m, 8H, ArH), 8.93 (d, 4H, β-pyrrole,³J=4.2 Hz), 8.98 (d, 4H, β-pyrrole); LD-MS calcd av mass 820.31, obsd819.6, 792.3 [M⁺ —CN], 761.5 [M⁺ —SCN], 703.3 [M⁺-2SCN], 626.0[M⁺-2SCN—C₆H₅], 613.5 [M⁺-2SCN—C₇H₇]; FAB-MS obsd 818.1275, calcd exactmass 818.1265 (C₄₈H₃₀N₆S₂Zn); λ_(abs) (toluene) 424, 550, 590 nm; λ_(em)(toluene) 599, 647 nm.

5,10,15,20-Tetrakis[m-(S-acetylthiomethyl)phenyl]porphyrin (29)

A solution of 101 mg of5,10,15,20-tetrakis[m-(bromomethyl)phenyl]porphyrin (Wen et al. (1997)J. Am. Chem. Soc., 119: 7726-7733, Karaman et al. (1992) J. Am. Chem.Soc., 114: 4889-4898) (102 μmol) and 60 mg of potassium thioacetate (525μmol) in 20 mL of THF was refluxed. After 5 h the mixture was cooled toroom temperature. 30 mL of water was added. The mixture was cooled toroom temperature and the phases were separated. The organic phase waswashed with 40 mL of 5% NaHCO₃ solution and dried (Na₂SO₄). Columnchromatography over flash silica gel with THF afforded a purple wax,which was purified by refluxing in hexanes. The mixture was filtered andthe residue was dissolved in CH₂Cl₂. The solvent was removed underreduced pressure, affording 63 mg (65 μmol, 63% yield) of a purplesolid. IR (neat) {tilde over (v)}=3423 (m, NH), 3318 (m, NH), 2963 (w,CH), 2926 (w, CH), 1690 (s, CO), 1600 (w), 1562 (w), 1540 (w), 1508 (w),1472 (w), 1420 (w), 1351 (w), 1132 (m), 1103 (w), 1018 (w), 997 (w), 957(w), 917 (w), 800 (m), 718 (m); ¹H NMR (300.5 MHz, CDCl₃): δ=-2.83 (s,2H, NH), 2.40 (s, 12H, CH₃), 4.41 (s, 8H, CH₂), 7.65-7.75 (m, 8H, ArH),8.06-8.17 (m, 8H, ArH), 8.84 (s, 8H, β-pyrrole); LD-MS calcd av mass966.2 (C₅₆H₄₆N₄O₄S₄), obsd 967.4, 925.3 [M⁺ —COCH₃], 892.2 [M⁺ —SCOCH₃],850.0 [M⁺ —SCOCH₃—COCH₃], 817.2 [M⁺−2SCOCH₃], 775.5 [M⁺-2SCOCH₃—COCH₃;λ_(abs) (toluene) 421, 515, 550, 591, 648 nm.

Zinc(II)-5,10,15,20-Tetrakis[m-(S-acetylthiomethyl)phenyl]porphyrin(Zn-29)

A mixture of 16.2 mg of 29 (16.7 μmol) in 20 mL of CHCl₃ and a solutionof 80.0 mg of Zn(OAc)₂.2H₂O (365 μmol) in 5 mL of methanol were combinedand stirred at ambient temperature. After 2 h the metalation wascompleted (checked by fluorescence excitation spectroscopy) and 40 mL ofH₂O was added. The phases were separated and the organic layer waswashed three times with 5% NaHCO₃ and dried (Na₂SO₄). The solvents wereremoved under reduced pressure. Column chromatography over flash silicagel with CH₂Cl₂/hexanes (4:1) gave the title compound as a purple solidin quantitative yield. IR (neat): {tilde over (v)}=2922 (w, CH), 2849(w, CH), 1690 (s, CO), 1655 (m, arom. C═C), 1600 (w, arom. C═C), 1478(w), 1420 (w), 1338 (w), 1208 (m), 1131 (m), 1067 (w), 1002 (m), 955(w), 932 (w), 794 (m), 717 (m); ¹H NMR (300.5 MHz, CDCl₃): δ=2.30 (s,12H, CH₃), 4.31 (s, 8H, CH₂), 7.62-7.69 (m, 8H, ArH), 8.05-8.13 (m, 8H,ArH), 8.92 (s, 8H, β-pyrrole); LD-MS calcd av mass 1028.15(C₅₆H₄₄N₄O₄S₄Zn), obsd 1028.8, 986.6 [M⁺ —COCH₃], 954.7 [M⁺ —SCOCH₃],911.3 [M⁺ —SCOCH₃—COCH₃], 880.4 [M⁺-2SCOCH₃], 838.8 [M⁺-2SCOCH₃—COCH₃],805.3 [M⁺-3SCOCH₃]; λ_(abs) (toluene) 424, 550, 589 nm; λ_(em) (toluene)597, 647 nm.

Cobalt(II)-5,10,15,20-Tetrakis[m-(S-acetylthiomethyl)phenyl]porphyrin(Co-29)

A mixture of 14.2 mg of 29 (14.7 μmol) in 20 mL of CHCl₃ and a solutionof 60.0 mg of Co(OAc)₂.4H₂O (339 μmol) in 5 mL of methanol were combinedand stirred at ambient temperature. After 5 h an additional 261.0 mg ofCo(OAc)₂.4H₂O (1.5 mmol) was added because there was still free baseporphyrin left. Stirring at room temperature was continued. After 20 hthe metalation was completed (checked by fluorescence excitationspectroscopy) and 30 mL of H₂O was added. The phases were separated andthe organic layer was washed three times with 5% NaHCO₃ and dried(Na₂SO₄). The solvents were removed under reduced pressure. Columnchromatography over flash silica gel with CH₂Cl₂/hexanes (5:1) gave thetitle compound as an orange-purple solid in quantitative yield. IR(neat): {tilde over (v)}=3037 (w, arom. CH), 2955 (w, CH), 2924 (m, CH),2849 (w, CH), 1725 (w), 1693 (s, CO), 1601 (w, arom. C═C), 1455 (w),1422,(w), 1350 (m), 1131 (m), 1003 (m), 957 (w), 796 (m), 714 (m); LD-MScalcd av mass 1023.16 (C₅₆H₄₄N₄O₄S₄Co), obsd 1023.4, 980.3 [M⁺ —COCH₃],948.3 [M⁺ —SCOCH₃], 875.2 [M⁺-2SCOCH₃]; λ_(abs) (toluene) 414, 529 nm.

Example 2 Setting and Reading the State of a Porphyrinic Macrocycle

I. Preparation of Gold Electrodes, Formation of Electrochemical Cell,Deposition of thiol-porphyrin Monolayer.

Glass slides were soaked in 90° C. piranha solution for thirty minutes,thoroughly rinsed with doubly distilled water, and dried under vacuum. A1 nm layer of chromium was evaporated onto the glass, followed by 100 mmof gold through a thin mask consisting of four parallel lines, each witha width of approximately 75 microns, spaced at approximately 1 mmintervals. All depositions were done at 10⁻⁶ torr using an E-beamevaporator.

Immediately after venting of the vacuum system, the slides were removedand stored under dry ethanol until use. The slides were dried with astream of nitrogen and a piece of PDMS with a 3 mm diameter hole in thecenter was immediately placed over all four gold electrodes and filledwith a porphyrin solution (0.1 mg per milliliter in dry ethanol) (Z-15from example 1).

The slide was then sonicated at room temperature for 15 minutes whichwas found to facilitate monolayer formation. After sonication, the PDMSmask was removed and the slide was rinsed with dry ethanol. A new PDMSmask was prepared by casting a 10:1 ratio solution of monomer tocatalyst into a mold consisting of a pyramidal channel with a 40 μm by 1cm base width. This new mask was placed on top of the porphyrin-coveredelectrodes to form the electrochemical cell. The channel was filled with1.0 M TBAP, and a silver wire reference electrode was used to completethe electrical circuit. This creates four identical porphyrin-coveredgold electrodes with 40 by 75 micron dimensions, each of which isindividually addressable using a common backplane reference electrode.The porphyrin monolayer was then analyzed with cyclic voltammetry toestablish that the porphyrin had bound to the gold substrate and toestablish the extent of coverage of the monolayer on the gold surface(FIG. 23).

II. Reading and Writing Porphyrin Bits.

A labview program was written to apply a potential pulse (the pulse wasapplied to the reference electrode, since the working electrode wasmaintained at ground potential). Thus, the potential was inverted andapplied to the reference electrode. The waveform was generated at 5 MHzand applied to a bare silver wire reference electrode. The currentresponse was monitored through the gold working electrode. The referenceelectrode was poised at a constant DC potential using a home builtpotentiostat that also amplifies the resulting current.

In order to write a bit into the porphyrin monolayer, it was necessaryto apply the appropriate potential to create the appropriate oxidationstate of the porphyrin. The reference electrode was poised at three DCpotentials while the working electrode was held at zero potential, inorder to probe the response at the neutral and at both non-neutraloxidation states of the porphyrin (FIG. 23). A 0-300 mV potential pulsewas applied below the first oxidation potential to record the backgroundcharging current. At 300 mV, there was no redox process occurring, thus,only the background charging current was observed. The electrode wasthen set at 500 mV DC and an identical 300 mV potential pulse wasapplied raising the potential to 800 mV and thereby eliciting the firstoxidation of the porphyrin.

This current response was the sum of the faradaic current superimposedon the background charging current. Because the background was constant,the first response could be subtracted from the latter and the remainderwas the faradaic current.

A second potential step was applied from 800-1100 mV. This step oxidizedthe porphyrin into the second oxidation state and produced a secondincrement of faradaic current which again was background subtracted. Thebackground subtracted currents had approximately equal magnitude becauseeach corresponded to a one electron processes in the same molecule(s)immobilized to the electrode surface. The amplified signal was acquiredat 5 MHz giving a time resolution of 200 ns per data point which wassufficient to detect the roughly 70 μs transient response. Thebackground-subtracted instantaneous current was integrated to produce aplot of the instantaneous charge as a function of time (FIG. 23).

Once the porphyrin was set at a given oxidation state, it could be readby applying the appropriate negative potential step. For example, thehigher bit could be read simply by stepping between 1100-800 mV. Thelower bit could be read by stepping between 800-500 mV. The chargingcurrent could be determined by stepping between 300-0 mV. Again, thebackground was subtracted from each step to determine thebackground-subtracted read current (FIG. 25). The read/write cycles areillustrated in FIG. 24.

Example 3 Tightly Coupled Porphyrin Arrays for Molecular Memory Storage

We have been developing approaches for molecular-based informationstorage where information is stored in the different oxidation states ofmolecular porphyrin arrays. To explore a simple design for suitablestorage molecules, we report here the synthesis of porphyrin arrayswhere porphyrins, having identical oxidation potentials, are directlylinked to one another instead of joined via a molecular linker.Oxidative coupling with AgPF₆ ofzinc(II)-5,15-bis(4-tert-butylphenyl)-10-phenylporphyrin, obtained by arational synthesis, afforded the expected meso,meso-linked dimer and anunexpected meso,meso,meso-linked trimer. For attachment to anelectroactive surface we synthesized a meso,meso-linked porphyrin dimerwith a thiol-linker in one of the meso-positions. The thiol-group wasprotected as thioacetyl moiety to avoid handling of free thiol groups.Coupling of zinc(II)-5,10,15-tris(3,5-di-tert-butylphenyl)porphyrin(“upper half”) andzinc(II)-10,20-bis(3,5-di-tert-butylphenyl)-5-[4-(S-acetylthio)phenyl]porphyrin(“bottom half”) afforded a set of three different meso,meso-linkeddimers with the desired one as the main product. Electrochemicalexamination of the meso,meso-linked dimer in solution showed that thecharge introduced upon oxidation of one of the porphyrin units shiftsthe oxidation potential of the adjacent porphyrin. Thereby two bits ofinformation can be stored in such a structure. No significant shift ofthe oxidation potentials was observed in the trimer in this instance.

Introduction.

In order to simplify the construction of the arrays for molecular basedinformation storage, we decided to synthesize porphyrin arrays where theporphyrins are directly linked to one another (Osuka and Shimidzu (1997)Angew. Chem. Int. Ed. Engl., 36: 135-137; Yoshida et al. (1998) Chem.Lett. 55-56; Nakano et al. (1998) Angew. Chem. Int. Ed. 37: 3023-3027;Senge and Feng (1999) Tetrahedron Lett. 40: 4165-4168). We expected thatthe juxtaposition of the porphyrins in the arrays would result in strong(“tightly”) coupling between the two constituents. This means that thecharge introduced upon oxidation of one of the porphyrin units shiftsthe oxidation potential of the adjacent porphyrin. In this manner,identical porphyrins can be used in the construction of themultiporphyrin array while still maintaining the ability to accessmultiple oxidation states.

Storing and retrieving information in redox-active molecules requires ameans of electrical communication from the macroscopic world to themolecular assemblies. One means of electrical communication involves theattachment of redox-active molecules via a thiol linker to anelectroactive surface such as gold (Zak et al. (1993) Langmuir 9:2772-2774; Postlethwaite et al. (1995) Langmuir 11: 4109-4116; Kondo etal. (1996) Thin Solid Films 284-285: 652-655; Simpson et al. (1996)Analyst 121: 1501-1505; Simpson et al. (1997) Langmuir 13: 460-464;Ishida et al. (1998) Chem. Lett. 267-268; Ishida et al. (1998) Chem.Commun. 57-58; Imahori et al. (1998) Langmuir 14: 5335-5338; Yanagida etal. (1998) Bull. Chem. Soc. Jpn. 71: 2555-2559). To overcome the problemof handling free thiol groups we decided to use protected thiol groups,especially after the report of Tour et al. that anS-acetylthio-substituted phenylethynyl oligomer underwent deprotectionin situ upon exposure to the gold surface (Tour et al. (1995) J. Am.Chem. Soc. 117: 9529-9534). Recently we have synthesized a number ofporphyrin monomers bearing one, two, or four protected thiol units andhave investigated the utility of a variety of different thiol protectinggroups (Gryko et al. (1999) J. Org. Chem. 64: 8634-8647).

In this example, we report the synthesis of five differentmeso,meso-linked porphyrin dimers and trimers. The electrochemicalproperties of the dimers and trimers have been investigated in solution.Two dimers bear acetyl protected thiol groups for attachment to goldsurfaces.

Results and Discussion.

Our first target molecule was a meso,meso-linked porphyrin dimer of twoidentical porphyrin monomers. With this molecule we wanted to test ifthe juxtaposition affords strong coupling between the two porphyrinunits, so that the redox potentials of the structurally identicalporphyrin units are shifted by a reasonable amount.

The preparation of the monomer utilized a new rational synthesis ofmeso-susbstituted porphyrins (Cho et al. (1999) J. Org. Chem. 64:7890-7901). Treatment of 5-phenyldipyrromethane (Littler et al. (1999)J. Org. Chem. 64: 1391-1396) with ethyl magnesium bromide followed byacylation with 4-tert-butylbenzoyl chloride led to the diacylateddipyrromethane 1 (Scheme 1, FIG. 26). Reduction with excess NaBH₄ inTHF/methanol afforded the corresponding diol, which was condensed withdipyrromethane (Lee and Lindsey (1994) Tetrahedron 50: 11427-11440;Littler et al. (1999) J. Org. Chem. 64: 1391-1396) under TFA catalysis.The desired porphyrin 2 was obtained in 35% yield as a purple solid.This synthesis route afforded the desired porphyrin with one freemeso-position without acidolytic scrambling. Porphyrin 2 is almostinsoluble in common solvents. Metalation with Zn(OAc)₂.2H₂O in refluxingCHCl₃ afforded Zn-2 in quantitative yield, which also has lowsolubility.

For the meso,meso-linked coupling of Zn-2 we used the method reported byOsuka et al. (Osuka and Shimidzu (1997) Angew. Chem. Int. Ed. Engl., 36:135-137) which employed AgPF₆ in a mixture of CHCl₃ and acetonitrile asthe oxidizing agent. Due to the low solubility of Zn-2 the reaction wasrun under reflux instead of room temperature. Using 0.5 mol equiv ofAgPF₆ as reported by Osuka et al., supra., led only to a small amount ofdimerization (˜10%, checked by analytical SEC). After addition ofanother 0.5 mol equiv of AgPF₆, quantitative conversion occurred within15 h. Because slight demetalation occurred under the couplingconditions, the crude mixture was again treated with Zn(OAc)₂.2H₂O. Weobtained two different oligomers, the expected dimer Zn-4 in 89% yieldand, surprisingly, also the trimer Zn-3 in 9% yield (Scheme 2, FIG. 27).Both are brown-purple solids and exhibit good solubility in commonsolvents. The substitution pattern of Zn-3 was confirmed by its ¹H NMRspectrum, which is almost identical with that of Zn-4 with addition of apeak due to the tert-butyl groups and the presence of the AA′BB′ patternfrom the protons of the central aryl groups. Such a spectrum arises froma symmetrical molecule and the suggested structure is the onlypossibility for Zn-3.

Electrochemical examination of porphyrin dimer Zn-4 revealed oxidationwaves at +0.49 and +0.66 V for the formation of the monocation of thetwo porphyrin units comprising porphyrin dimer Zn-4. This is to becompared with the single oxidation wave for the corresponding porphyrinmonomer, which is expected at 0.58 V. The appearance of two waves inporphyrin dimer Zn-4 indicates that the oxidation of the first porphyrinunit, forming the monocation, shifts the oxidation potential of thesecond porphyrin unit to higher potential. A similar potential shiftoccurred for the second oxidation of each porphyrin unit (Table 1). Theelectrochemical examination of porphyrin trimer Zn-3 showed that onlythe oxidation potentials of the central porphyrin unit are shifted bythe neighboring units. The two terminal porphyrin units do notsignificantly influence the oxidation potentials of each other andoverlapping of the waves was observed.

Driven by the positive results for the porphyrin dimer Zn-4 we decidedto synthesize a meso,meso-linked porphyrin dimer bearing a thiol linkerfor attachment to a gold surface. To improve the solubility of themonomers we chose 3,5-di-tert-butylphenyl groups as substituents for thenon-linking meso-positions.

The “bottom” porphyrin Zn-8 with the S-acetyl protected thiol group wassynthesized in a similar way as for monomer Zn-2. Diacylation ofdipyrromethane (Littler et al. (1999) J. Org. Chem. 64: 1391-1396) with3,5-di-tert-butylbenzoyl chloride afforded dipyrromethane 7 as a whitepowder after crystallization (Scheme 3, FIG. 28). For the synthesis ofdipyrromethane 6 there are at least two conceivable pathways. The firstattempt to synthesize this molecule involved reaction of commerciallyavailable 4-methylthiobenzaldehyde with pyrrole to give thecorresponding dipyrromethane (Gryko et al. (1999) J. Org. Chem. 64:8634-8647). However, subsequent treatment with sodium tert-butoxide(Pinchart et al. (1999) Tetrahedron Lett. 40: 5479-5482), followed byquenching of the anion with acetyl chloride did not afford the desiredproduct (equation 1, FIG. 29). In this situation we decided to changeour strategy. Thus reaction of 4-S-acetylthiobenzaldehyde (Gryko et al.(1999) J. Org. Chem. 64: 8634-8647) with pyrrole afforded dipyrromethane6 in 62% yield (equation 2, FIG. 30). Reduction of 7 to thecorresponding diol and condensation with 6 under TFA catalysis yieldedporphyrin 8 in 10% yield, accompanied by disulfide 9 in 3% yield.Metalation of 8 with Zn(OAc)₂.2H₂O gave Zn-8 as a purple solid in 90%yield. Disulfide 9 was metalated likewise, affording Zn-9 in 60% yieldas an orange-purple solid (Scheme 4, FIG. 31).

The synthesis of the “top” porphyrin Zn-10 was done using the samemethod as before but in much better yield. Reduction of the diacylateddipyrromethane 7 with NaBH₄ and condensation of the resulting diol with5-(3,5-di-tert-butylphenyl)dipyrromethane (Imahori et al. (1999) Bull.Chem. Soc. Jpn, 72: 485-502) under TFA catalysis afforded porphyrin 10as a purple solid in 21% yield (Scheme 5, FIG. 32). Metalation withZn(OAc)₂.2H₂O led to Zn-10 as a red-purple solid in quantitative yield.Zn-10, like all the other porphyrin monomers (8, Zn-8 and 10) anddisulfides (9 and Zn-9) bearing 3,5-di-tert-butylphenyl groups in themeso-positions, exhibits good solubility in common solvents.

Coupling of Zn-8 and Zn-10 with AgPF₆ in refluxing CHCl₃ afforded theexpected three dimers in almost quantitative yield. Traces of higheroligomers were also present. After remetalation with Zn(OAc)₂.2H₂O weobtained porphyrin dimers Zn-11, Zn-12 and Zn-13 in 30%, 44% and 23%yield, respectively (Scheme 6, FIG. 33). All porphyrin dimers are purplesolids with good solubility in common solvents. Under these reactionconditions the acetylthio group remained intact.

Conclusion.

Various meso,meso-linked porphyrin dimers and trimers have beensynthesized. The electrochemical studies of the dimers in solutionrevealed a shift of the oxidation potential for the generation of themonocation of the second porphyrin unit after oxidation of the firstporphyrin unit. This shift in the oxidation potentials of the individualporphyrin units provides an opportunity to access distinct and differentoxidation potentials in a dimeric array where each porphyrin unit isidentical. The effect was small in the trimers tested herein.

Experimental.

General

All reactions involving porphyrin formation and transformation wereperformed with shielding from ambient light. All chemicals obtainedcommercially were used as received unless noted otherwise. Reagent gradesolvents (CH₂Cl₂, CHCl₃, hexanes, ethyl ether, ethyl acetate) and HPLCgrade solvents (acetonitrile, toluene) were used as received fromFisher. THF was distilled from sodium/benzophenone. All reported NMRspectra were obtained at 300 MHz. UV-Vis absorption and fluorescencespectra were recorded in toluene. Flash chromatography was performed onflash silica (Baker, 200-400 mesh) or alumina (Fisher, 80-200 mesh).Mass spectra were obtained via laser desorption (LD-MS) in the absenceof an added matrix using a Bruker Proflex II mass spectrometer, fastatom bombardment (FAB-MS) using a JEOL HX110HF mass spectrometer (ionsource 40° C., CsKI or polyethylene glycol standards, 10 ppm elementalcompositional accuracy for the porphyrins), or electron-impact massspectrometry (EI-MS). Porphyrin metalation was monitored by fluorescenceexcitation and emission spectroscopy. Preparative scale size exclusionchromatography (SEC) was performed using BioRad Bio-Beads SX-1 withtoluene as eluent. The chromatography was performed with gravity flow.Analytical scale SEC was performed with a Hewlett-Packard 1090 HPLCusing a 1000 Å column (5 μL, styrene-divinylbenzene copolymer) with THFas eluent.

General Procedure for Metal Insertion

A solution of porphyrin in CHCl₃ or CH₂Cl₂ and a solution/suspension ofthe metal acetate in methanol were combined and stirred. After themetalation was completed (checked by fluorescence excitationspectroscopy), H₂O was added. The phases were separated and the organiclayer was washed three times with 5% NaHCO₃ and dried (Na₂SO₄). Thesolvents were removed under reduced pressure. Purification was done bycolumn chromatography over flash silica gel.

1,9-Bis(4-tert-butylbenzoyl)-5-phenyldipyrromethane (1)

To a solution of 5-phenyldipyrromethane (Lee and Lindsey (1994)Tetrahedron 50: 11427-11440; Littler et al. (1999) J. Org. Chem. 64:1391-1396) (2.22 g, 10 mmol) in toluene (200 mL) stirred under argon andcooled in a water bath was slowly added a solution of ethyl magnesiumbromide (1 M solution in THF, 50 mL, 50 mmol). The resultingbrown-orange mixture was stirred for 30 min. Then a solution of4-tert-butylbenzoyl chloride (4.9 mL, 25.1 mmol) in toluene (25 mL) wasadded dropwise. The solution became darker and was stirred for 1 h afterthe addition was completed. Then the reaction was quenched with satd aqNH₄Cl (100 mL). Ethyl acetate (100 mL) was added and the phases wereseparated. The organic phase was washed with water, 2 M aq NaOH, waterand brine and then dried (Na₂SO₄). The solvents were removed underreduced pressure and the residue was filtered through a pad of silicaand eluted with CH₂Cl₂/ethyl acetate 10:1. The solvents were againremoved under reduced pressure and the brown residue was purified bycolumn chromatography (1^(st) column: alumina, hexanes —CH₂Cl₂/hexanes—CH₂Cl₂—CH₂Cl₂/MeOH; 2^(nd) column: silica, ethyl ether/hexanes 1:2;3^(rd) column: silica: CH₂Cl₂/ethyl acetate 5:1), affording 2.96 g (5.5mmol, 55%) as a brown solid. mp 133° C.; IR (neat): {tilde over(v)}=3438, 3251, 2963, 2903, 2868, 1611, 1556, 1479; ¹H NMR (300.5 MHz,CDCl₃): δ=1.34 (s, 18H), 5.67 (s, 1H), 6.00 (dd, 2H, ³J=3.7 Hz, ⁴J=2.9Hz), 6.64 (dd, 2H, ³J=3.7 Hz, ⁴J=2.2 Hz), 7.30-7.51 (m, 5H), 7.42, 7.73(AA′,BB′, 2×4H), 11.04 (br, s, 2H); ¹³C NMR (75.6 MHz, CDCl₃, ATP):δ=31.1 (−), 34.9 (+), 44.9 (−), 111.0 (−), 120.6 (−), 124.9 (−), 127.3(−), 128.8 (−), 129.2 (−), 129.5 (−), 131.0 (+), 135.6 (+), 140.5 (+),140.8 (+), 155.0 (+), 184.3 (+); EI obsd 542, 527, 465, 409, 381, 316;Anal. Calcd. for C₃₇H₃₈N₂O₂: C, 81.88; H, 7.06; N, 5.16. Found: C,81.79; H, 7.22; N, 5.21.

5,15-Bis(4-tert-butylphenyl)-10-phenylporphyrin (2)

To a solution of 1 (500 mg, 921 μmol) in a 1:2 mixture of methanol/THF(27 mL) was added NaBH₄ (1.74 g, 46 mmol) in several portions. Themixture was stirred for 2.5 h, then quenched with water (40 mL) andextracted with CH₂Cl₂. The organic phase was dried (K₂CO₃) and thesolvents were removed under reduced pressure. The yellow residue anddipyrromethane (Littler et al. (1999) J. Org. Chem. 64: 1391-1396) (135mg, 923 μmol) were then dissolved in acetonitrile and stirred at roomtemperature in the dark. Then TFA (852 μL, 11.1 mmol) was added and thesolution turned dark immediately. After 20 min DDQ (630 mg, 2.8 mmol)was added because the yield did not increase any further (checked byoxidizing an aliquot with DDQ and quantifying with UV/VIS spectroscopy).After stirring for 1.5 h the mixture was filtered through a pad ofalumina and eluted with CH₂Cl₂. The solvents were removed under reducedpressure and the residue was dissolved in a mixture of CH₂Cl₂/hexanes1:1. Purification by column chromatography (silica, CH₂Cl₂/hexanes 1:1—CH₂Cl₂) afforded 211 mg (324 μmol, 35%) of a purple solid. IR (neat):{tilde over (v)}=3312, 3030, 2957, 2864, 1596, 1560, 1500; ¹H NMR (300.5MHz, CDCl₃): δ=-2.99 (s, 2H), 1.62 (s, 18H), 7.70-7.82 (m, 3H), 7.78,8.18 (AA′,BB′, 2×4H), 8.14-8.24 (m, 2H), 8.85 (d, 2H, ³J=5.1 Hz), 8.95(d, 2H, ³J=5.1 Hz), 9.06 (d, 2H, ³J=4.4 Hz), 9.33 (d, 2H, ³J=4.4 Hz),10.20 (s, 1H); LD-MS obsd 649.9; FAB-MS obsd 650.3416, calcd exact mass650.3409 (C₄₆H₄₂N₄); λ_(abs) (toluene) 415, 509, 543, 586, 641 nm.

Zinc(II)-5,15-bis(4-tert-butylphenyl)-10-phenylporphyrin (Zn-2)

A suspension of 2 (112 mg, 172 μmol) in CHCl₃ (50 mL) and a solution ofZn(OAc)₂.2H₂O (3.78 g, 172 mmol) in methanol (10 mL) were combined andrefluxed 2 h. The solvents were removed under reduced pressure to afford123 mg (172 μmol, 100%) of a bright purple solid. IR (neat): {tilde over(v)}=3081, 3022, 2956, 1498; ¹H NMR (300.5 MHz, CDCl₃): δ=1.63 (s, 18H),7.71-7.83 (m, 3H), 7.78, 8.17 (AA′BB′, 2×4H), 8.20-8.25 (m, 2H), 8.96(d, 2H, ³J=5.1 Hz), 9.04 (d, 2H, ³J=5.1 Hz), 9.14 (d, 2H, ³J=4.4 Hz),10.25 (s, 1H); LD-MS obsd 714.1; FAB-MS obsd 712.2565, calcd exact mass712.2544 (C₄₆H₄₀N₄Zn); λ_(abs) (toluene) 419, 544, 582 nm; λ_(em)(toluene) 592, 639 nm.

Meso-meso-meso porphyrin trimer Zn-3 and meso-meso porphyrin dimer Zn-4

To a suspension of Zn-2 (31.1 mg, 43.5 μmol) in CHCl₃ (20 mL) was addeda solution of AgPF₆ (5.5 mg, 21.8 μmol) in acetonitrile (3 mL). Themixture was refluxed for 8 h. Then more AgPF₆ (5.5 mg, 21.8 μmol) wasadded because the reaction stopped (monitored by analytical SEC). Afteran additional 15 h the reaction was quenched with water (30 mL). Thephases were separated and the organic phase was washed with water anddried (Na₂SO₄). The solvents were removed under reduced pressure. Thebrown-purple solid was dissolved again in CHCl₃ (30 mL). A solution ofZn(OAc)₂.2H₂O (290 mg, 1.3 mmol) in methanol (7 mL) was added and themixture was stirred for 3 h in the dark. Then the reaction was quenchedwith water and the phases were separated. The organic phase was washedthree times with 5% aq NaHCO₃ and dried (Na₂SO₄). The solvents wereremoved under reduced pressure and the residue was dissolved in aminimum amount of toluene. Purification by preparative SEC with tolueneafforded 2.8 mg of the meso,meso,meso-trimer (1.4 μmol, 9% yield) as abrown solid and 27.6 mg of the meso,meso-dimer (19.3 μmol, 89% yield) asa brown-purple solid. Zn-3: IR (neat): {tilde over (v)}=2959, 2922,2854, 1542, 1458; ¹H NMR (300.5 MHz, CDCl₃): δ=1.54 (s, 18H), 1.56 (s,36H), 7.59, 8.15 (AA′BB′, 2×4H), 7.70, 8.18 (AA′BB′, 2×8H), 7.78-7.85(m, 6H), 8.15-8.22 (m, 4H), 8.23 (d, 4H, ³J=4.4 Hz), 8.30-8.36 (m, 4H),8.76 (d, 4H), ³J=4.4 Hz), 8.77 (d, 4H, ³J=4.4 Hz), 9.03 (d, 4H, ³J=4.4Hz), 9.07 (d, 4H, ³J=4.4 Hz); LD-MS obsd 2056.8 [M⁺], 2000.7 [M⁺-^(t)Bu]; FAB-MS obsd 2062.68, calcd exact mass 2062.70(C₁₃₂H₁₁₂N₁₂Zn₃); λ_(abs) (toluene) 419, 477, 567 nm; λ_(em) (toluene)641, 664 nm; Zn-4: IR (neat):=2958, 2868, 1558, 1488; ¹H NMR (300.5 MHz,CDCl₃): δ=1.52 (s, 36H), 7.67, 8.15 (AA′BB′, 2×8H), 7.74-7.86 (m, 6H),8.18-8.20 (m, 4H), 8.31 (d, 4H, ³J=3.7 Hz), 8.71 (d, 4H, ³J=4.4 Hz),9.01 (d, 4H, ³J=4.4 Hz), 9.04 (d, 4H, ³J=4.4 Hz); LD-MS obsd 1423.7;FAB-MS obsd 1422.48, calcd exact mass 1422.49 (C₉₂H₇₈N₈Zn₂); λ_(abs)(toluene) 421, 459, 561 nm; λ_(em) (toluene) 634, 659 nm.

5-[4-Methylthiophenyl]dipyrromethane (5)

Pyrrole (50.0 mL, 720 mmol) and 4-methylthiobenzaldehyde (3.83 mL, 28.8mmol) were added to a 250 mL flask and degassed with a stream of argon.Then TFA (0.22 mL) was added and the mixture was stirred under argon atroom temperature for 5 min and quenched with 0.1 M NaOH. Ethyl acetatewas then added and the phases were separated. The organic phase waswashed with water and dried (Na₂SO₄). Then the solvent was removed undervacuum to afford an orange oil. Bulb-to-bulb distillation (200° C., 0.01mmHg) gave a yellow oil. The oil was dissolved in EtOH and addition of asmall amount of water afforded white crystals (5.00 g, 64.7%). mp 94-95°C.; ¹H NMR 8 2.51 (s, 3H), 5.43 (s, 1H), 5.95 (s, 2H), 6.21 (m, 2H),6.69 (m, 2H), 7.17, 7.25 (AA′BB′, 2×2H), 7.87 (br, s, 2H); ¹³C NMR δ16.6, 44.1, 108.0, 109.2, 118.1, 127.6, 129.6, 133.1, 137.7, 139.8;EI-MS obsd 268.1033 (M⁺), calcd exact mass 268.1034; Anal. Calcd. forC₁₆H₁₆N₂S: C, 71.60; H, 6.01; N, 10.44; S, 11.95. Found: C, 71.60; H,5.99; N, 10.31; S, 11.81.

5-[4-(S-Acetylthio)phenyl]dipyrromethane (6)

Pyrrole (34.0 mL, 489 mmol) and 4-(S-acetylthio)benzaldehyde ((Gryko etal. (1999) J. Org. Chem. 64: 8634-8647) (3.50 g, 19.4 mmol) were addedto a 100 mL flask and degassed with a stream of argon. Then TFA (0.15mL, 1.94 mmol) was added and the mixture was stirred under argon at roomtemperature for 5 min and quenched with DIEA (0.330 mL, 1.94 mmol). Allvolatile materials were evaporated under high-vacuum. The crude mixturewas filtered through a pad of silica to afford a yellow oil, which wasdissolved in EtOH and allowed to stand at −20° C. for 3 days. Yellowishcrystals were isolated by filtration. The filtrate was concentrated, asmall amount of water was added and the mixture was allowed to stand at−20° C. for a few days, affording a second crop of crystals (3.56 g,62.0%). mp 100-101° C.; ¹H NMR δ 2.44 (s, 3H), 5.40 (s, 1H), 5.90 (s,2H), 6.18 (m, 2H), 6.62 (m, 2H), 7.20, 7.34 (AA′BB′, 2×2H), 7.97 (br, s,2H); ¹³C NMR δ 31.0, 44.3, 108.2, 108.9, 118.3, 126.8, 130.1, 132.8,135.3, 144.7, 195.7; EI-MS obsd 296.0996 (M⁺), calcd exact mass296.0983; Anal. calcd. for C₁₇H₁₆N₂OS: C, 68.89; H, 5.44; N, 9.45; S,10.82. Found: C, 68.69; H, 5.56; N, 9.39; S, 10.91.

1,9-Bis(3,5-di-tert-butylbenzoyl)dipyrromethane (7)

To a solution of dipyrromethane (Littler et al. (1999) J. Org. Chem. 64:1391-1396) (421 mg, 2.9 mmol) in toluene (60 mL) stirred under argon andcooled in a water bath was slowly added a solution of ethyl magnesiumbromide (1 M solution in THF, 14.4 mL, 14.4 mmol). The resultingbrown-orange mixture was stirred for 30 min at ambient temperature.3,5-Di-tert-butylbenzoic acid was refluxed in thionyl chloride in thepresence of 1 vol % DMF. A colorless liquid, bp 167° C. (water suctionpump) was obtained in 89% yield. A solution of 3,5-di-tert-butylbenzoylchloride (1.82 g, 7.2 mmol) in toluene (8 mL) was added dropwise to thebrown-orange mixture. The solution became darker and was stirred for 2 hafter the addition was completed. Then the reaction was quenched withsatd aq NH₄Cl (30 mL). Ethyl acetate (60 mL) was added and the phaseswere separated. The organic phase was washed with water, 2 M aq NaOH,water and brine and then dried (Na₂SO₄). The solvents were removed underreduced pressure and the residue was filtered through a pad of silicaand eluted with CH₂Cl₂/ethyl acetate 6:1-5:3. The solvents were againremoved under reduced pressure and the residue was dissolved in a smallamount of ethyl acetate. Hexanes was added until turbidity occurred. Themixture was cooled overnight at −20° C. and filtered, affording 442 mg(0.8 mmol, 27%) of a white powder. mp 220° C.; IR (neat): {tilde over(v)}=3263, 2963, 1607, 1582, 1485; ¹H NMR (300.5 MHz, CDCl₃): δ=1.32 (s,36H), 4.27 (s, 2H), 6.17-6.13 (m, 2H), 6.71-6.77 (m, 2H), 7.57 (s, 4H),11.47 (br, s, 2H); ¹³C NMR (75.6 MHz, CDCl₃, ATP): δ=26.8 (+), 31.3 (−),34.9 (+), 110.0 (−), 121.1 (−), 123.6 (−), 125.6 (−), 131.2 (+), 137.5(+), 138.0 (+), 150.5 (+), 185.6 (−); Anal. Calcd. for C₃₉H₅₀N₂O₂: C,80.93; H, 8.71; N, 4.84. Found: C, 80.69; H, 8.72; N, 4.85.

10,20-Bis(3,5-di-tert-butylphenyl)-5-[4-(S-acetylthio)phenyl]porphyrin(8)

To a solution of 7 (397 mg, 686 μmol) in a 1:2 mixture of methanol/THF(21 mL) under argon was added NaBH₄ (1.30 g, 34 mmol) in severalportions. The mixture was stirred for 2.5 h, then quenched with water(40 mL) and extracted with CH₂Cl₂. The organic phase was dried (K₂CO₃)and the solvents were removed under reduced pressure. The yellow foamobtained and 5-[4-(S-acetylthio)phenyl]dipyrromethane 6 (204 mg, 686μmol) were dissolved in acetonitrile and stirred at room temperature.Then TFA (640 μL, 8.3 mmol) was added and the solution immediatelyturned dark blue. After 25 min DDQ (467 mg, 2.1 mmol) was added becausethe yield did not increase any further (checked by oxidizing an aliquotwith DDQ and quantifying with UV/VIS spectroscopy). After 1.5 h themixture was filtered through a pad of alumina and eluted with CH₂Cl₂.The solvents were removed under reduced pressure and the residue waspurified by column chromatography on silica (1^(st) column:CH₂Cl₂/hexanes 1:4-1:1, 2^(nd) column: CH₂Cl₂/hexanes 1:2). Twofractions of brown-purple solids were obtained, yielding 14 mg of thedisulfide 9 (9 μmol, 3% yield) and 57 mg of 8 (68 μmol, 10% yield). 9:IR (neat): {tilde over (v)}=3316, 2961, 2924, 2854, 1592, 1466; ¹H NMR(300.5 MHz, CDCl₃): δ=-2.94 (s, 4H), 1.52 (s, 72H), 7.79 (t, 4H, ⁴J=1.5Hz), 8.10, 8.30 (AA′BB′, 2×4H), 8.10 (d, 8H, ⁴J=1.5 Hz), 8.94 (d, 4H,³J=5.1 Hz), 8.96 (d, 4H, ³J=5.1 Hz), 9.07 (d, 4H, ³J=5.1 Hz), 9.34 (d,4H, ³J=4.4 Hz), 10.22 (s, 2H); LD-MS obsd 1589.4 [M⁺], 793.4 [M⁺/2];FAB-MS obsd 1586.87, calcd exact mass 1586.86 (C₁₀₈H₁₁₄N₈S₂); λ_(abs)(toluene) 417, 511, 544, 586, 642 nm. 8: IR (neat): {tilde over(v)}=3307, 2958, 2861, 1708, 1590, 1467; ¹H NMR (300.5 MHz, CDCl₃):δ=−2.95 (s, 2H), 1.55 (s, 36H), 2.60 (s, 3H), 7.81, 8.28 (AA′BB′, 2×2H),7.82 (t, 2H, ⁴J=1.5 Hz), 8.12 (d, 4H, ⁴J=1.5 Hz), 8.88 (d, 2H, ³J=5.1Hz), 8.97 (d, 2H, ³J=5.1 Hz), 9.08 (d, 2H, ³J=5.1 Hz), 9.35 (d, 2H,³J=4.4 Hz), 10.2 (s, 1H); LD-MS obsd 837.2 [M⁺], 852.2 [M⁺+15 ], 809.2[M⁺ —CO], 795.1 [M⁺ —COCH₃]; FAB-MS obsd 836.4503, calcd exact mass836.4488 (C₅₆H₆₀N₄OS); λ_(abs) (toluene) 416, 510, 544, 585, 641 nm.

Zinc(II)-10,20-Bis(3,5-di-tert-butylphenyl)-5-[4-(S-acetylthio)phenyl]porphyrin(Zn-8)

A solution of 6 (56 mg, 172 μmol) in CHCl₃ (20 mL) and a solution ofZn(OAc)₂.2H₂O (734 mg, 3.3 mmol) in methanol (5 mL) were combined andstirred 6.5 h. Purification by column chromatography (silica,CH₂Cl₂/hexanes 1:1) afforded 54 mg (60.0 μmol, 90%) of a purple solid.IR (neat): {tilde over (v)}=3066, 2956, 1703, 1675, 1590, 1469; ¹H NMR(300.5 MHz, CDCl₃): δ=1.55 (s, 36H), 2.59 (s, 3H), 7.79, 8.28 (AA′BB′,2×2H), 7.82 (t, 2H, ⁴J=2.2 Hz), 8.12 (d, 4H, ⁴J=2.2 Hz), 8.99 (d, 2H,³J=4.4 Hz), 9.06 (d, 2H, ³J=4.4 Hz), 9.17 (d, 2H, ³J=4.4 Hz), 9.43 (d,2H, ³J=4.4 Hz), 10.29 (s, 1H); LD-MS obsd 900.1, 915.2 [M⁺+15], 872.0[M⁺ —CO], 857.9 [M⁺ —COCH₃]; FAB-MS obsd 898.3617, calcd exact mass898.3623 (C₅₆H₅₈N₄OSZn); λ_(abs) (toluene) 420, 545, 583 nm; λ_(em)(toluene) 591, 640 nm.

Zinc(II)-Disulfide Zn-9

A solution of 9 (14 mg, 8.8 μmol) in CHCl₃ (5 mL) and a solution ofZn(OAc)₂.2H₂O (193 mg, 879 μmol) in methanol (2 mL) were combined andstirred. After 7 h an additional 194 mg (879 μmol) of Zn(OAc)₂.H₂O wasadded and stirring was continued for 15.5 h. Purification by columnchromatography (silica, CH₂Cl₂/hexanes 1:2) afforded 9.0 mg (5.2 μmol,60%) of an orange-purple solid. IR (neat): {tilde over (v)}=3067, 2959,2923, 2862, 1592, 1468; ¹H NMR (300.5 MHz, CDCl₃): δ=1.51 (s, 72H), 7.78(s, 4H), 8.10, 8.30 (AA′BB′, 2×4H), 8.10 (s, 8H), 9.05 (s, 8H), 9.16 (d,4H, ³J=4.4 Hz), 9.42 (d, 4H, ³J=4.4 Hz), 10.28 (s, 2H); LD-MS obsd1716.6, 871.2 [M⁺/2+15], 856.2 [M⁺/2], 751.9 [M⁺ —S-^(t)Bu-Me]; FAB-MSobsd 1710.71, calcd exact mass 1710.69 (C₁₀₈H₁₁₀N₈S₂Zn²); λ_(abs)(toluene) 421, 545, 585 nm; λ_(em) (toluene) 594, 641 nm.

5,10,15-Tris(3,5-di-tert-butylphenyl)porphyrin (10)

To a solution of 7 (578 mg, 1.0 mmol) in a 1:2 mixture of methanol/THF(30 mL) under argon was added NaBH₄ (1.89 g, 50 mmol) in severalportions. The mixture was stirred for 2 h, then quenched with water (60mL) and extracted with CH₂Cl₂. The organic phase was dried (K₂CO₃) andthe solvents were removed under reduced pressure. The resulting orangeoil and crude 5-(3,5-di-tert-butylphenyl)dipyrromethane (Imahori et al.(1999) Bull. Chem. Soc. Jpn, 72: 485-502) (334 mg, 1.0 mmol) weredissolved in acetonitrile and stirred at room temperature. Then TFA (930μL, 12.1 mmol) was added and the solution immediately turned dark blue.After 25 min DDQ (680 mg, 3.0 mmol) was added because the yield did notincrease any further (checked by oxidizing an aliquot with DDQ andquantifying with UV/VIS spectroscopy). After 75 min the solution wasfiltered through a pad of alumina and eluted with CH₂Cl₂. The solventswere removed under reduced pressure and the residue was purified bycolumn chromatography (silica, CH₂Cl₂/hexanes 1:4-1:2), affording 183 mg(209 μmol, 21% yield) a purple solid. IR (neat): {tilde over (v)}=3305,3064, 2958, 1588, 1468; ¹H NMR (300.5 MHz, CDCl₃): δ=-2.91 (s, 2H), 1.51(s, 18H), 1.55 (s, 36H), 7.79 (t, 1H, ⁴J=1.5 Hz), 7.81 (t, 2H, ⁴J=2.2Hz), 8.07 (d, 2H, ⁴J=1.5Hz), 8.12 (d, 2H, ⁴J=2.2Hz), 8.92 (d, 2H, ³J=5.1Hz), 8.96 (d, 2H, ³J=5.1 Hz), 9.07 (d, 2H, ³J=4.4 Hz), 9.34 (d, 2H,³J=5.1 Hz), 10.20 (s, 1H); LD-MS obsd 875.7; FAB-MS obsd 874.5935, calcdexact mass 874.5913 (C₆₂H₇₄N₄); λ_(abs) (toluene) 416, 510, 544, 585,641 nm.

Zinc(II)-5,10,15-Tris(3,5-di-tert-butylphenyl)porphyrin (Zn-10)

A solution of 10 (177 mg, 202.2 μmol) in CHCl₃ (40 mL) and a solution ofZn(OAc)₂.2H₂O (2.22 g, 10.1 mmol) in methanol (10 mL) were combined andstirred 21 h. Purification by column chromatography (silica,CH₂Cl₂/hexanes 1:2) afforded 187 mg (199.2 μmol, 99%) of a red-purplesolid. IR (neat): {tilde over (v)}=3060, 2960, 2872, 1591, 1470; ¹H NMR(300.5 MHz, CDCl₃): δ=1.52 (s, 18H), 1.54 (s, 36H), 7.78 (t, 1H, ⁴J=1.5Hz), 7.81 (t, 2H, ⁴J=1.5 Hz), 8.08 (d, 2H, ⁴J=1.5 Hz), 8.12 (d, 2H,⁴J=1.5Hz), 9.03 (d, 2H, ³J=4.4 Hz), 9.06 (d, 2H, ³J=4.4 Hz), 9.15 (d,2H, ³J=4.4 Hz), 9.41 (d, 2H, ³J=5.1 Hz), 10.27 (s, 1H); LD-MS obsd937.6, 951.8 [M⁺+15], 752.1 [M⁺-3 ^(t)Bu-Me]; FAB-MS obsd 936.5057,calcd exact mass 936.5048 (C₆₂H₇₂N₄Zn); λ_(abs) (toluene) 419, 545 nm;λ_(em) (toluene) 591, 639 nm.

Meso-Meso Porphyrin Dimers Zn-11, Zn-12 and Zn-13

To a solution of Zn-8 (15.9 mg, 17.7 μmol) and Zn-10 (16.6 mg, 17.7μmol) in CHCl₃ (20 mL) was added a solution of AgPF₆ (8.9 mg, 35.2 μmol)in acetonitrile (3 mL). The mixture was refluxed for 7 h. Then moreAgPF₆ (15 mg, 59.3 μmol) was added because the reaction stopped(monitored by analytical SEC). After an additional 22 h an additional 22mg (87.0 μmol) of AgPF₆ was added because the reaction stopped again.Refluxing was continued for 19 h and then the reaction was quenched withwater (30 mL). The phases were separated and the organic phase waswashed with water and dried (Na₂SO₄). The solvents were removed underreduced pressure. The dark purple solid was dissolved in CHCl₃ (30 mL).A solution of Zn(OAc)₂.2H₂O (390 mg, 1.8 mmol) in methanol (7 mL) wasadded and the mixture was stirred for 3 h in the dark. Then the reactionwas quenched with water (50 mL) and the phases were separated. Theorganic phase was washed three times with 5% aq NaHCO₃ and dried(Na₂SO₄). The solvents were removed under reduced pressure and theresidue was dissolved in a minimum amount of toluene. Purification bypreparative SEC followed by column chromatography (silica,CH₂Cl₂/hexanes 1:2-2:3) afforded 9.9 mg of Zn-11 (5.3 μmol, 30% yield)as an orange solid, 14.3 mg of Zn-12 (7.8 μmol, 44% yield) as ared-purple solid and 7.3 mg of Zn-13 (4.1 μmol, 23% yield) as abrown-purple solid. Zn-11: IR (neat): {tilde over (v)}=3060, 2956, 2861,1592, 1465; ¹H NMR (300.5 MHz, CDCl₃): δ=1.43 (s, 72H), 1.57 (s, 36H),7.68 (t, 4H, ⁴J=2.2 Hz), 7.83 (t, 2H, ⁴J=1.4 Hz), 8.08 (d, 8H, ⁴J=2.2Hz), 8.15 (d, 4H, ³J=4.4 Hz), 8.30 (d, 4H, ⁴J=1.4 Hz), 8.71 (d, 4H,³J=4.4 Hz), 9.04 (d, 4H, ³J=4.4 Hz), 9.08 (d, 4H, ³J=5.1 Hz); LD-MS obsd1877.1; FAB-MS obsd 1870.87, calcd exact mass 1870.99 (C₁₂₄H₁₄₂N₈Zn₂);λ_(abs) (toluene) 421, 460, 561 nm; λ_(em) (toluene) 625, 660 nm. Zn-12:IR (neat): {tilde over (v)}=3069, 2955, 1700, 1588, 1465; ¹H NMR (300.5MHz, CDCl₃): δ=1.43 (s, 36H), 1.44 (s, 36H), 1.57 (s, 18H), 7.66-7.72(m, 4H), 7.82 (t, 1H, ⁴J=2.2 Hz), 7.85, 8.37 (AA′BB′, 2×2H), 8.09 (d,8H, ⁴J=1.5 Hz), 8.12 (d, 2H, ³J=5.1 Hz), 8.17 (d, 2H, ⁴J=2.2 Hz), 8.17(d, 2H, ³J=4.4 Hz), 8.71 (d, 2H, ³J=5.1 Hz), 8.72 (d, 2H, ³J=5.1 Hz),9.02-9.07 (m, 6H), 9.08 (d, 2H, ³J=4.4 Hz); LD-MS obsd 1423.7; FAB-MSobsd 1832.85, calcd exact mass 1832.85 (C₁₁₈H₁₂₈N₁₆OSZn₂); λ_(abs)(toluene) 420, 460, 561 nm; λ_(em) (toluene) 626, 660 nm. Zn-13: IR(neat): {tilde over (v)}=2919, 1702, 1561, 1461; ¹H NMR (300.5 MHz,CDCl₃): δ=1.44 (s, 72H), 7.70 (t, 4H, ⁴J=1.5 Hz), 7.85, 8.37 (AA′BB′,2×4H), 8.09 (d, ⁴J=1.5 Hz), 8.14 (d, 4H, ³J=4.4 Hz), 8.72 (d, 4H, ³J=51Hz), 9.03 (d, 4H, ³J=5.1 Hz), 9.05 (d, 4H, ³J=5.1 Hz); LD-MS obsd1801.1, 1816.3 [M⁺+15], 1772.9 [M⁺ —CO], 1758.9 [M⁺ —COCH₃], 1715.8[M⁺-2COCH₃]; FAB-MS obsd 1794.62, calcd exact mass 1794.71(C₁₁₂H₁₁₄N₈O₂S₂Zn₂); λ_(abs) (toluene) 421, 461, 561 nm; λ_(em)(toluene) 626, 659 nm.

Example 4 Synthesis of “Porphyrin-Linker-Thiol” Molecules with DiverseLinkers for Studies of Molecular-Based Information Storage

The attachment of redox-active molecules such as porphyrins to anelectroactive surface provides an attractive approach for electricallyaddressable molecular based information storage. Porphyrins are readilyattached to a gold surface via thiol linkers. The rate of electrontransfer between the electroactive surface and the porphyrin is one ofthe key factors that dictates suitability for molecular-based memorystorage. This rate depends on the type and length of the linkerconnecting the thiol unit to the porphyrin. In this example, we examinedthe effects of different linkers. We have developed different routes forthe preparation of thiol-derivatized porphyrins with various linkers.Three of the linkers contain alkyne groups (S-phenylethynyl,S-phenylethynylphenyl and S-methylphenylethynylphenyl), four have alkylunits (S-methylphenyl, S-ethylphenyl, S-propylphenyl and S-hexyl) andone has four fluorine atoms attached directly to the thiophenyl unit. Tofacilitate the synthesis of the porphyrins, convenient routes have beendeveloped to a wide range of aldehydes possessing a protectedS-acetylthio group. An efficient synthesis of1-iodo4-(S-acetylthio)benzene also has been developed. A set ofporphyrins each bearing one S-acetyl derivatized linker at one mesoposition and mesityl moieties at the three remaining meso positions hasbeen synthesized. Altogether seven new aldehydes, eight free baseporphyrins and eight zinc porphyrins have been prepared. The zincporphyrins bearing the different linkers all form self-assembledmonolayers (SAMs) on gold via in situ cleavage of the S-acetylprotecting group. The SAM of each of the porphyrins is electrochemicallyrobust and exhibits two reversible oxidation waves.

This example describes thiol-derivatized porphyrins containing diverselinkers designed to explore how the linker affects the rates of writingand reading as well as duration of information storage (i.e., memorypersistence). The studies reported here from the methods described abovefor the synthesis of thiol-derivatized porphyrin monomers for studies ofmolecular-based information storage. In various embodiments of thiswork, porphyrins bearing one thiol group were designed for verticalorganization on a gold surface, while porphyrins bearing two or fourthiol groups were designed for horizontal arrangement on a gold surface.The redox potentials were tuned through variation in the mesosubstituents and/or the central metal. The different meso substituentscan also give rise to altered packing patterns of the molecules in aself-assembled monolayer (SAM). Thiol protecting groups were examinedfor compatibility with the reactions for porphyrin-formation, metalinsertion, Pd-coupling to form multiporphyrin arrays, and in situdeprotection on a gold surface. The S-acetylthio protecting group gavethe best overall results (including in situ cleavage on gold) and hasbeen used in almost all of our subsequent work.

The synthetic methodology described above is used herein to prepare aset porphyrins, each bearing one thioacetate group and three mesitylgroups. These molecules are designed for vertical organization on a goldsurface. One prototypical example, incorporates a thiol-derivatizedp-phenylene unit (linker A, FIG. 34). This molecule binds to a goldelectrode and exhibits facile electronic communication with the goldsurface. The p,p′-diphenylethyne unit (linker B, FIG. 34) increases thedistance of the porphyrin from the gold surface, potentially slowingwriting/reading rates, though linkers of this type are known to provideefficient hole transport (Seth et al. (1994) J. Am. Chem. Soc., 116:10578-10592; Seth (1996) J. Am. Chem. Soc., 118: 11194-11207). A similarstructure with one additional methylene unit (linker C, FIG. 34)provides a test of whether a conjugated connection (e.g., a directthiophenyl attachment) is essential. An electron-deficient p-phenylenelinker is provided by linker D (FIG. 34). The effects of a progressiveincrease in the alkyl character of the linker can be examined bycomparison of linkers A, E, F, G and H (FIG. 34). Finally, anethynylphenyl linker (I) is employed to achieve direct conjugation tothe porphyrin (Anderson (1994) Inorg. Chem., 33: 972-9811; Lin (1994) J.Science, 264, 1105-1111). The use of these porphyrins as memory storageentities will be reported elsewhere.

Results and Discussion.

A large number of porphyrin monomers bearing free thiols or S-acetylderivatized thiols have been prepared. The traditional method ofsynthesis involves the derivatization of a substituted porphyrin with athiol reagent or protected thiol unit. The emergence of mild conditionsfor preparing porphyrins has made possible those strategies wheresensitive or elaborate substituents are incorporated in the aldehydeprecursor to the porphyrin (Lindsey (2000) In The Porphyrin Handbook;Kadish, K. M.; Smith, K. M.; Guilard, R., Eds.; Academic Press, SanDiego, Calif., Vol. 1, pp 45-118; Lindsey (1997) In Modular Chemistry,Michl, J. Ed., NATO ASI Series C: Mathematical and Physical Sciences,Vol. 499, Kluwer Academic Publishers: Dordrecht, pp. 517-528, Lindsey(1994) Tetrahedron, 50: 8941-8968; Ravikanth (1998) Tetrahedron, 54:7721-7734). This latter approach has been explored using S-acetylprotected thio-derivatized benzaldehydes, which are converted to therespective porphyrin with the protecting group intact (Nishimura (1999)J. Electroanal. Chem., 473: 75-84; Gryko et al. (1999) J. Org. Chem.,64, 8635-8647; Kuroda (1989) J. Am. Chem. Soc., 111: 1912-1913; Jagessarand Tour (2000) Org. Lett., 2: 111-113). The advantages of introducingthe S-acetylthio moiety at the aldehyde stage are as follows. (1)Synthetic manipulation of the porphyrins is minimized. (2) The polarityimparted by the S-acetylthio moiety facilitates separation of thedesired porphyrin from a mixed aldehyde condensation. (3) Purificationat the aldehyde stage is often more straightforward than separation ofporphyrin mixtures. For those molecules where the linker is constructedusing a Pd coupling reaction (e.g., diphenylethyne), the reactionconditions for use with aldehydes (high concentration, inclusion of CuI)afford superior results compared with those with porphyrins (Wagner etal. (1999) Chem. Mater., 11: 2974-2983). Thus we have opted to introducethe S-acetyl protected thiol unit at the aldehyde stage throughout thiswork.

Synthesis of Aldehydes.

The synthesis of aldehydes possessing a thioacetate group utilizedseveral different approaches. Five of the aldehydes possess an alkylthiol unit and three contain an aryl thiol unit. The former are usuallyobtained by straightforward reaction of an alkyl halide and a thiolreagent (thioacetate, thiourea), while the latter (S-protected or freethiol form) are often obtained with more difficulty. The few knownmethods for preparing aryl thiols, from aryl sulfides or aryl halides,generally require harsh conditions. Thus, we searched for new approachesfor incorporating the S-acetyl group in arenes. The S-acetyl group iscompatible with a variety of reaction conditions, including those inporphyrin formation and Pd-mediated iodo-ethyne couplings (Gryko et al.(1999) J. Org. Chem., 64, 8635-8647), but is labile in the presence ofbases (e.g., NEt₃, alumina) if attached to an arene.

The structures of aldehydes 4 and 8 (FIG. 38 and FIG. 39, respectively)suggested an obvious method of synthesis via Pd-coupling of4-iodobenzaldehyde with 1-[4-(S-acetylthio)phenyl]acetylene (3) or1-[4-(S-acetylthiomethyl)phenyl]acetylene (7). The synthesis of compound3 utilizes 1-iodo-4-(S-acetylthio)benzene 1 (Scheme 1, FIG. 40). Wefound the previously reported procedures (Pearson and Tour (1997) J.Org. Chem., 62: 1376-1387; Hsung et al. (1995) Tetrahedron Lett., 26:4525-4528) of this starting material to require tedious purification. Insearching for a more efficient pathway to this key molecule, theselective transformation of 1-fluoro-4-iodobenzene into1-iodo-4-(S-acetylthio)benzene using conditions developed by Tiecco andcoworkers (Tiecco et al. (1982) Synthesis, 478-480; Testaferri et al.(1983) Synthesis, 751-755) was attempted. However, we obtained aninseparable mixture of products, regardless of the temperature and theamount of MeSNa used. Sita and coworkers converted pipsyl chloride(4-iodobenzenesulfonyl chloride) to 1-iodo-4-mercaptobenzene (Hsung etal. (1995) Organometallics, 14: 4808-4815). We adopted this attractiveroute but with the use of the non-aqueous conditions for reduction ofsulfonyl chlorides recently reported by Uchiro and Kobayashi (Uchiro andKobayashi (1999) Tetrahedron Lett., 40: 3179-3182), thereby obtaining amuch higher yield. Thus, pipsyl chloride was successfully reduced to1-iodo-4-mercaptobenzene which upon in situ treatment with acetylchloride gave the desired 1-iodo-4-(S-acetylthio)benzene (1, 85%) afterstraightforward chromatographic purification (Scheme 1, FIG. 40). Thezinc chloride formed in the first step is a likely catalyst of theacylation in the second step. The iodobenzene 1 obtained in this mannerwas successfully converted into the ethyne derivative 3 usingestablished procedures (Pearson and Tour (1997) J. Org. Chem., 62:1376-1387; Hsung et al. (1995) Tetrahedron Lett., 26: 4525-4528).Pd-coupling of 3 and 4-iodobenzaldehyde smoothly afforded aldehyde 4 in90% yield. As noted by Sita and coworkers (Hsung et al. (1995)Tetrahedron Lett., 26: 4525-4528), it is essential to use a hinderedamine such as N,N-diisopropylethylamine instead of triethylamine toobtain satisfactory yields in all Pd-coupling reactions involving theS-acetylthiophenyl group.

The synthesis of aldehyde 8 proceeded along a similar strategy (Scheme2, FIG. 41). Treatment of 4-(bromomethyl)-1-iodobenzene with thioacetateunder very mild conditions (Zheng et al. (1999) Tetrahedron Lett. 40:603-606) gave 5, which upon Pd-coupling with trimethylsilylacetyleneafforded the building block bearing two protecting groups (6).Deprotection of the TMS group in 6 gave 7, which upon Pd-mediatedcoupling with 4-iodobenzaldehyde furnished aldehyde 8. Each reaction inthis sequence afforded high yields.

The next target aldehyde was4-(S-acetylthio)-2,3,5,6-tetrafluorobenzaldehyde (9) (FIG. 35). Thefluorine atom in the para position of pentafluorobenzenes is known to bevery reactive toward nucleophilic substitution. Indeed,pentafluorophenyl-substituted porphyrins were recently reported toundergo fluoro-substitution by alkyl thiols (Shaw et al. (1999)Tetrahedron Lett. 40: 1595-1596; Shaw et al. (1999) Tetrahedron Lett.40: 7585-7586). This result encouraged us to attempt a similarsubstitution of pentafluorobenzaldehyde with thioacetate usingconditions resembling those used in the reaction of potassiumthioacetate with benzyl halides. After a vigorous reaction we found thatthe substrate had vanished, and the only product was a very polarsubstance which bound at the origin of TLC (silica, CH₂Cl₂). We surmisedthat the latter molecule might be the anion of4-mercapto-2,3,5,6-tetrafluorobenzaldehyde (formed by thioester cleavagefollowing nucleophilic substitution), and upon treatment with acetylchloride the desired aldehyde 9 was obtained in 69% yield afterchromatography.

The synthesis of aldehyde 10 was accomplished using the strategydescribed herein 3-(S-acetylthiomethyl)benzaldehyde and also describedin Gryko et al. (199) J. Org. Chem. 64: 8635-8647. Reduction of thecommercially available 4-(bromo-methyl)benzonitrile with DIBALH gave thecorresponding 4-(bromomethyl)benzaldehyde (Wen and Schlenoff (1997) Am.Chem. Soc. 119: 7726-7733; Bookser and Bruice (1991) Am. Chem. Soc. 113:4208-4218; Wagner et al. (1997) Tetrahedron 53: 6755-6790 for thesynthesis of 3-(bromomethyl)benzaldehyde). Substitution of the bromidewith potassium thioacetate gave the desired S-acetyl protectedthiobenzaldehyde 10 in good yield (FIG. 36).

Aldehyde 11 was synthesized by radical addition (Lub et al. (1997)Liebigs Ann. Recueil, 2281-2288) of thioacetic acid to4-vinylbenzaldehyde. Vinyl benzaldehyde was synthesized by the procedureof Ren et al. (1993) Bull. Chem. Soc. Jpn. 66: 1897-1902 with thefollowing changes: The addition of DMF was performed at a 38 mmol scaleat 0° C. Purification by column chromatography (silica, Et₂O/hexanes,1:3) afforded 4-vinylbenzaldehyde in 60% yield (FIG. 37)/

The homologous aldehyde 15 with a propyl rather than ethyl unit wassynthesized starting from 4-bromobenzaldehyde (Scheme 3, FIG. 42).Protection of the carbonyl group as the cyclic acetal 12 (Hewlins et al.(1986) J. Chem. Res. (M), 8: 2645-2696), conversion to the correspondingGrignard reagent and in situ reaction with allyl bromide furnishedintermediate 13. Radical addition with thioacetic acid afforded acetal14, which was easily hydrolyzed to the respective aldehyde 15 (overallyield 18% from 4-bromobenzaldehyde).

The aliphatic aldehyde 17 should be accessible via the same procedure asused for aldehyde 10. However, reduction of 7-bromoheptanitrile with 1eq of DIBALH gave only ˜50% conversion to aldehyde 16, probably due tocompeting deprotonation of the protons α- to the nitrile group.Therefore we chose to synthesize 16 by oxidation of 7-bromo-1-heptanolwith PCC (Enders and Bartzen (1991) Liebigs Ann. Chem, 569-574).Treatment of crude aldehyde 16 with potassium thioacetate affordedaldehyde 17 as a yellow oil in 51% yield (overall yield 42% from7-bromo-1-heptanol) (FIG. 38).

The shortest and most promising strategy for the synthesis of porphyrin26 involves the preparation of 3-[4-(S-acetylthio)phenyl]propynalfollowed by mixed-aldehyde condensation, rather than attempting thePd-mediated coupling of an iodo or ethynyl porphyrin. Due to theinstability of propynal, we performed a Pd-coupling of commerciallyavailable propiolaldehyde diethylacetal with1-iodo-4-(S-acetylthio)benzene (1) (FIG. 39). The desired acetal 18 wasobtained in 62% yield.

It is noteworthy that in each strategy employed, the S-acetyl protectinggroup and the sulfur atom were incorporated in one step, or the thiolwas protected in situ with an acetyl group without workup andpurification. In so doing the handling of free thiols was avoided whileworking with a wide range of thiol-derivatized compounds.

Synthesis of Porphyrins

The investigation of porphyrins oriented in a vertical manner on anelectroactive surface can be achieved by the synthesis of porphyrinsbearing a p-thioaryl or ω-thioalkyl unit at one meso position. SuchA₃B-porphyrins were prepared using a two-step, one-flask synthesis offacially-encumbered meso-substituted porphyrins that is compatible withdiverse ortho-disubstituted benzaldehydes (Lindsey and Wagner (1989) J.Org. Chem., 54: 828-836). A mixed-aldehyde condensation ofmesitaldehyde, a thiol-protected aldehyde and pyrrole afforded a mixtureof porphyrins, from which the desired thiol-protected A₃B-porphyrin wasobtained by chromatography. The polarity imparted by the thioacetategroup enabled facile separation of the mixture of porphyrins.

In this manner, aldehydes 4, 8, 9, 10, 11, 15 and 17 were converted tothe thiol-protected A₃B-porphyrins 19-25, respectively, in yields of7-22% (Scheme 4, FIG. 43). It is noteworthy that purification of most ofthe porphyrins was achieved by silica pad filtration followed by onecolumn chromatography (or centrifugal preparative TLC) operation. Thissame approach was applied to acetal 18 but the yield of the desired A₃Bporphyrin was only 0.8% (Scheme 5, FIG. 44). We attribute the low yieldin part to the competitive Michael reaction of pyrrole and the activatedalkyne. The corresponding zinc chelates Zn-19-Zn-26 were obtained byreaction of the free base porphyrins 19-26 with Zn(OAc)₂.2H₂O (Chart 1).In each case, zinc insertion occurred without altering the thiolprotecting groups.

Electrochemical Studies

The electrochemical behavior of the Zn porphyrins was investigated forsamples both in solution and self-assembled on gold. The solutionelectrochemistry of each of the porphyrins is similar to that previouslyreported for other aryl-substituted Zn porphyrins.² In particular, eachporphyrin exhibits two reversible oxidation waves. The E_(1/2) valuesfor all the porphyrins in solution are similar to one another(E_(1/2)(1)˜0.58 V; E_(1/2)(2)˜0.86 V; versus Ag/Ag⁺; E_(1/2)FeCp₂/FeCp₂ ⁺=0.19 V), with the exception of Zn-21 and Zn-26. TheE_(1/2) values for Zn-21 are shifted ˜0.1 V more positive due tofluorination of one of the porphyrin aryl groups. The E_(1/2) values forZn-26 are shifted ˜0.1 V more negative due to the presence of theconjugating meso-alkynyl group. The porphyrins bearing the differentlinkers all form self-assembled monolayers (SAMs) on gold via in situcleavage of the S-acetyl protecting group. The SAM of each of theporphyrins is electrochemically robust and exhibits two reversibleoxidation waves. The two oxidation waves of the Zn porphyrin SAMs werewell resolved, as is the case for the Zn porphyrins in solution.However, the two E_(1/2) values of the Zn-20 and Zn-23 SAM are eachshifted ˜0.10-0.15 V more positive than those observed in solution. Thissame behavior is observed for the SAMs of the other Zn porphyrins. Thepositive shifts in redox potentials observed upon formation of theporphyrin SAMs are consistence with the results of previous experimentson other electroactive species (e.g., thiol-derivatized ferrocenes) ongold (Creager and Rowe (1994) J. Electroanal. Chem. 370: 203-211).

CONCLUSIONS

The introduction of an S-acetyl protected thiol unit in an aldehydeenables the corresponding porphyrin to be prepared without handling freeporphyrin thiols. The combination of a few simple strategies providedaccess to a broad range of thiol-derivatized aldehydes. A set ofporphyrins has been prepared for vertical organization via one linker onan electroactive surface. The S-acetyl protecting group cleaves in situwhen the porphyrin contacts a gold surface. The porphyrins form SAMsthat exhibit robust, reversible electrochemistry. Collectively, thestudies indicated that all of the linker architectures examined aresuitable candidates for molecular information storage elements.

Experimental

General

All chemicals obtained commercially were used as received unlessotherwise noted. Reagent grade solvents (CH₂Cl₂, CHCl₃, hexanes, Et₂O,acetone) and HPLC grade solvents (acetonitrile, toluene) were used asreceived from Fisher. Pyrrole was distilled from CaH₂. All reported NMRspectra were collected in CDCl₃ (¹H NMR at 300 MHz; ¹³C NMR at 75 MHz)unless noted otherwise. UV-Vis absorption and fluorescence spectra wererecorded in CH₂Cl₂ or toluene as described previously. Flashchromatography was performed on flash silica (Baker, 200-400 mesh) oralumina (Fisher, 80-200 mesh). Mass spectra were obtained via laserdesorption (LD-MS) in the absence of an added matrix,⁵⁵ fast atombombardment (FAB-MS, 10 ppm elemental compositional accuracy for theporphyrins), or electron-impact mass spectrometry (EI-MS). ACS gradechloroform containing 0.75% of ethanol was used in all porphyrin formingreactions. Porphyrin metalation was monitored by fluorescence emissionand excitation spectroscopy. 4-Iodobenzaldehyde and1-bromomethyl-4-iodobenzene were obtained from Karl Industries, Ltd.

1-Iodo-4-(S-acetylthio)benzene (1)

Following a general procedure (Uchiro and Kobayashi (1999) TetrahedronLett., 40: 3179-3182), to a stirred suspension of zinc powder (3.80 g,58.0 mmol) and dichlorodimethylsilane (7.00 mL, 58.0 mmol) in1,2-dichloroethane (126 mL) was added a solution of4-iodobenzenesulfonyl chloride (5.00 g, 16.5 mmol) andN,N-dimethylacetamide (4.60 mL, 50.0 mmol) in dichloroethane (126 mL).The mixture was stirred at 75° C. for 2 h until the zinc powder was nolonger visible. The reaction mixture was cooled to 50° C. and acetylchloride (1.53 mL, 21.5 mmol) was added. After 15 min the mixture waspoured into water. The water layer was extracted with CH₂Cl₂ and thecombined organic layers were dried (Na₂SO₄), filtered and evaporated.The colorless oil thus obtained was chromatographed (silica,CH₂Cl₂/hexanes, 1:4) affording a colorless oil (3.93 g, 85.0%) whichsolidified at −20° C. mp 56-57° C. (lit. 54-55° C.)⁴³; ¹H NMR δ 2.42 (s,3H), 7.12, 7.73 (AA′BB′, 2×2H); ¹³C NMR δ 31.0, 96.7, 128.4, 136.7,139.0, 193.9; Anal. Calcd. for C₈H₇IOS: C, 34.55; H, 2.54; I, 45.63; S,11.53. Found: C, 34.69; H, 2.59; I, 45.52; S, 11.59.

2-(4-Formylphenyl)-1-[4-(S-acetylthio)phenyl]acetylene (4)

Samples of 4-iodo-benzaldehyde (660 mg, 2.80 mmol), 3 (500 mg, 2.80mmol), CuI (29 mg, 15 μmol) and Pd(PPh₃)₂Cl₂ (13 mg, 18 μmol) wereplaced in a Schlenk flask. The flask was evacuated for 3 min then theflask was backflushed with argon for 3 min. The process of evacuationand flushing was repeated 3 times. At this point the argon flow rate wasincreased and the threaded stopcock was removed. Deareated THF (5.0 mL)and DIEA (5.0 mL) were added in succession to the flask by gastightsyringe. The threaded stopcock was replaced, the argon flow rate wasreduced and the flask was immersed in an oil bath thermostated at 40° C.The reaction was stopped after 40 h. The mixture was then filtered andevaporated. The resulting orange-brown solid was chromatographed(silica, CH₂Cl₂/hexanes, 2:3, then 1:1, then 3:2) to affordyellowish-white crystals, which upon recrystallization (ethylacetate/heptane) afforded 707 mg (90.2%) of white crystals. mp 128-129°C. (lit. 122-123° C.)³⁶; ¹H NMR 6 2.65 (s, 3H), 7.63, 7.79 (AA′BB′,2×2H), 7.87, 8.07 (AA′BB′, 2×2H), 10.22 (s, 1H); ¹³C NMR δ 31.2, 91.0,93.5, 124.5, 129.9, 130.0, 130.5, 133.1, 133.2, 135.2, 136.5, 192.3,194.1; FAB-MS obsd 280.0551, calcd exact mass 280.0558; Anal. Calcd. forC₁₇H₁₂O₂S: C, 72.83; H, 4.31; S, 11.44. Found: C, 72.66; H, 4.39; S,11.52.

1-Iodo-4-(S-acetylthiomethyl)benzene (5)

Following a general procedure (Zheng et al. (1999) Tetrahedron Lett. 40:603-606), potassium thioacetate (2.20 g, 19.3 mmol) was added to asolution of 4-(bromomethyl)-1-iodobenzene (4.80 g, 16.2 mmol) inanhydrous N,N-dimethylacetamide (15 mL). The mixture was stirredovernight at rt, poured into water, and extracted with CH₂Cl₂. Thecombined organic extracts were washed with water, dried (Na₂SO₄) andevaporated. The resulting brown oil was distilled (90° C., 0.005 mmHg)to obtain a pale-yellow solid which solidified after a few days (4.68 g,99%). mp 40-41° C.; ¹H NMR δ 2.37 (s, 3H), 4.07 (s, 2H), 7.07, 7.64(AA′BB′, 2×2H); ¹³C NMR δ 31.09, 33.6, 93.5, 131.6, 138.2, 138.4, 195.5;FAB-MS obsd 291.9425, calcd exact mass 291.9419; Anal. Calcd. forC₉H₉IOS: C, 37.00; H, 3.11; I, 43.44; S, 10.98. Found: C, 37.39; H,3.13; I, 43.04; S, 11.26.

1-[4-(S-Acetylthiomethyl)phenyl)]-2-(trimethylsilyl)acetylene (6)

Samples of 5 (2.92 g, 10.0 mmol), CuI (105 mg, 553 μmol) andPd(PPh₃)₂Cl₂ (46 mg, 66 μmol) were placed in a Schlenk flask. The flaskwas evacuated for 3 min and then the flask was backflushed with argonfor 3 min. The process of evacuation and flushing was repeated 3 times.At this point the argon flow rate was increased and the threadedstopcock was removed. Deareated THF (10.0 mL) and DIEA (10.0 mL) wereadded in succession to the flask by gastight syringe. Nexttrimethylsilylacetylene (2.00 ml, 14.0 mmol) was added. The threadedstopcock was replaced, the argon flow rate was reduced and the flask wasimmersed in an oil bath thermostated at 40° C. The reaction was stoppedafter 40 h. The mixture was then filtered and evaporated. The resultingorange-brown solid was chromatographed (silica, CH₂Cl₂/hexanes, 1:4,then 3:7) to afford a slightly yellow oil which solidified upon standingat rt (2.40 g, 91.8%). mp 41-42° C.; ¹H NMR δ 0.23 (s, 9H), 2.32 (s,3H), 4.07 (s, 2H), 7.21, 7.36 (AA′BB′, 2×2H); ¹³C NMR δ 0.7, 31.0, 33.9,95.1, 105.5, 122.8, 129.4, 132.8, 138.9, 195.4; FAB-MS obsd 262.0839,calcd exact mass 262.0848; Anal. Calcd. for C₁₄H₁₈SiOS: C, 64.07; H,6.91; S, 12.22. Found: C, 64.02; H, 6.99; S, 12.23.

1-[4-(S-Acetylthiomethyl)phenyl]acetylene (7)

To a solution of 6 (2.52 g, 9.60 mmol) in THF (30 mL) was added aceticacid (0.2 mL) and acetic anhydride (0.2 mL). The mixture was cooled to−20° C. and a solution of Bu₄NF (2.40 g, 9.60 mmol) in THF (20 mL) wasadded dropwise during 5 min. The reaction mixture was kept at −20° C.for another 10 min then poured on a silica pad and eluted withCH₂Cl₂/hexanes (1:1). The solvents were removed under reduced pressureand the residue was dissolved in CH₂Cl₂, dried (Na₂SO₄) and evaporated,affording a yellowish oil (1.69 g, 92.3%). ¹H NMR δ 2.13 (s, 3H), 2.88(s, 1H), 3.88 (s, 2H), 7.02, 7.20 (AA′BB′, 2×2H); ¹³C NMR δ 30.8, 33.6,83.8, 121.5, 129.3, 132.8, 139.0, 195.3; EI-MS obsd 190.0458, calcdexact mass 190.0452 (C₁₁H₁₀OS).

2-(4-Formylphenyl)-1-[(4-(S-acetylthiomethyl)phenyl)acetylene (8)

Samples of 4-iodobenzaldehyde (1.18 g, 5.00 mmol), 7 (950 mg, 5.00mmol), CuI (52 mg, 270 μmol) and Pd(PPh₃)₂Cl₂ (23 mg, 33 μmol) wereplaced in a Schlenk flask. The flask was evacuated via vacuum pump for 3min and then the flask was backflushed with argon for 3 min. The processof evacuation and flushing was repeated 3 times. At this point the argonflow rate was increased and the threaded stopcock was removed. DeareatedTHF (5.0 mL) and DIEA (5.0 mL) were added in succession to the flask bygastight syringe. The threaded stopcock was replaced, the argon flowrate was reduced and the flask was immersed in an oil bath thermostatedat 40° C. The reaction was stopped after 40 h. The mixture was thenfiltered and evaporated. The resulting orange-brown solid waschromatographed (silica, CH₂Cl₂/hexanes, 2:3, then 1:1, then 3:2) toafford yellowish-white crystals. Recrystallization (ethylacetate/heptane) gave 1.30 g (88.2%) of white crystals. mp 128-129° C.;¹H NMR δ 2.49 (s, 3H), 4.07 (s, 2H), 7.25, 7.43 (AA′BB′, 2×2H), 7.59,7.79 (AA′BB′, 2×2H), 9.95 (s, 1H); ¹³C NMR δ 30.9, 33.9, 89.5, 93.9,122.1, 129.8, 130.1, 130.2, 132.7, 132.7, 136.1, 139.5, 192.0, 195.4;FAB-MS obsd 294.0717, calcd exact mass 294.0715; Anal. Calcd. forC₁₈H₁₄O₂S: C, 73.44; H, 4.79; S, 10.89. Found: C, 73.18; H, 4.82; S,10.88.

2,3,5,6-Tetrafluoro-4-(S-acetylthio)benzaldehyde (9)

Potassium thioacetate (1.28 g, 11.2 mmol) was added to a solution ofpentafluorobenzaldehyde (1.24 mL, 10.2 mmol) in anhydrous DMA (20 mL).After a strong exotherm subsided, the mixture was stirred at rt for 30min. Acetyl chloride (1.60 mL, 22.4 mmol) was added and the mixture wasstirred for another 30 min, then poured into water and extracted twicewith ethyl ether. The combined organic extracts were dried (Na₂SO₄) andevaporated to obtain an orange oil which was chromatographed (silica,CH₂Cl₂/hexanes, 2:3) affording a pale-yellow solid. Recrystallizationfrom heptane gave white crystals (1.77 g, 69%). mp 86-87° C.; ¹H NMR δ2.53 (s, 3H), 10.30 (s, 1H); ¹³C NMR δ 30.9, 115.5, 117.2, 145.3, 148.7,182.9, 187.9; FAB-MS obsd 252.9936, calcd exact mass 252.9946; Anal.Calcd. for C₉H₄F₄O₂S: C, 42.86; H, 1.60; S, 12.72. Found: C, 43.00; H,1.71; S, 12.67.

4-(S-Acetylthiomethyl)benzaldehyde (10)

To a solution of 4-(bromomethyl)-benzaldehyde (Hsung et al. (1995)Organometallics, 14: 4808-4815; Bookser and Bruice (1991) Am. Chem. Soc.113: 4208-4218; Wagner et al. (1997) Tetrahedron 53: 6755-6790 for thesynthesis of 3-(bromomethyl)benzaldehyde) (0.43 g, 2.2 mmol) in acetone(10 mL) was added potassium thioacetate (280 mg, 2.5 mmol) understirring at rt, then the mixture was refluxed. A precipitate formedafter a few minutes. The reaction was monitored by TLC and cooled to rtwhen no starting material was detectable (3.5 h). Water (25 mL) wasadded, the mixture was extracted with ethyl acetate (3×30 mL), and thecombined organic phases were dried (Na₂SO₄) and evaporated. Columnchromatography over flash silica gel (ethyl ether/hexanes, 1:1) gave 359mg (85% yield) of a brown oil which darkened upon standing (nonethelesselementary analysis four weeks after exposure to air at rt indicated ahigh level of purity as listed below). IR (neat): {tilde over (v)} 3052,2923, 2830, 2737, 1694, 1606, 1576; ¹H NMR δ 2.36 (s, 3H), 4.15 (s, 2H),7.45, 7.81 (AA′BB′, 2×2H), 9.97 (s, 1H); ¹³C NMR (APT) δ 30.1 (−), 32.9(+), 129.3 (−), 129.9 (−), 135.2 (+), 144.7 (+), 191.5 (−), 194.3 (+);GC-MS (EI) obsd 194, 152, 119, 91, 43; Anal. Calcd for C₁₀H₁₀O₂S: C,61.83; H, 5.19; S, 16.51. Found: C, 61.97; H, 5.20; S, 16.60.

4-[2-(S-Acetylthio)ethyl]benzaldehyde (11)

Following a general procedure (Lub et al. (1997) Liebigs Ann. Recueil,2281-2288), 4-vinylbenzaldehyde (Vinyl benzaldehyde was synthesized bythe procedure of Ren et al. (1993) Bull. Chem. Soc. Jpn. 66: 1897-1902with the following changes: The addition of DMF was performed at a 38mmol scale at 0° C. Purification by column chromatography (silica,Et₂O/hexanes, 1:3) afforded 4-vinylbenzaldehyde in 60% yield.) (1.15 g,8.70 mmol) and thioacetic acid (2.20 mL, 30.8 mmol) were dissolved intoluene (20 mL) and the solution was purged with argon for 15 min. ThenAIBN (20 mg) was added and the mixture was heated to 90° C. After 2 hmore AIBN (160 mg) was added. This was repeated after one additionalhour. 2 h later AIBN (100 mg) was added again and the mixture was heatedfor one additional hour. Then aq NaHCO₃ (10%, 50 mL) was added and thephases were separated. The aqueous phase was washed with ether and thecombined organic phases were dried (Na₂SO₄). Purification by columnchromatography (silica, ether/hexanes, 1:3) gave an orange oil, whichsolidified and darkened upon standing at −20° C. to give a black solid(983 mg, 54%), which was pure enough for further reactions. A smallsample was recrystallized from refluxing heptane to afford colorlessplates. mp 35° C.; IR (neat): {tilde over (v)} 3029, 2929, 2828, 2737,1699, 1606, 1578; ¹H NMR δ 2.34 (s, 3H), 2.96 (t, ³J=8.1 Hz, 2H), 3.15(t, ³J=8.1 Hz, 2H), 7.40, 7.83 (AA′BB′, 2×2H), 9.99 (s, 1H); ¹³C NMR(APT) δ 30.5 (+), 31.3 (−), 36.5 (+), 129.0 (−), 129.7 (−), 134.7 (+),146.8 (+), 191.5 (−), 194.9 (+); GC-MS (EI) obsd 208, 166, 133, 120, 91,77, 43; Anal. Calcd for C₁₁H₁₂O₂S: C, 63.43; H, 5.81; S, 15.40. Found:C, 63.63; H, 5.90; S, 15.62.

2-(4-Bromophenyl)-5,5-dimethyl-1,3-dioxane (12)

The following describes an improved procedure at three times largerscale in much shorter time compared with the literature (Hewlins et al.(1986) J. Chem. Res. (M), 8: 2645-2696). 4-Bromobenzaldehyde (3.00 g,16.2 mmol), neopentylglycol (1.86 g, 17.9 mmol) and p-toluenesulfonicacid (50 mg, 0.3 mmol) were dissolved in toluene (30 mL) and thesolution was refluxed for 3 h. Then the solution was cooled to rt,washed twice with aq NaHCO₃ (10%), twice with water and dried (Na₂SO₄).The solvent was evaporated and the oily residue was crystallized fromhexanes, affording colorless needles (2.81 g, 64%). ¹³C NMR (APT) δ 21.7(−), 22.9 (−), 30.1 (+), 77.5 (+), 100.8 (−), 122.7 (+), 127.8 (−),131.3 (−), 137.5 (+).

2-(4-Allylphenyl)-5,5-dimethyl-1,3-dioxane (13)

In a dry apparatus a solution of 12 (2.05 g, 7.60 mmol) in THF (15 mL)was added dropwise to magnesium powder (0.22 g, 9.1 mmol) under argon.After the addition was completed the mixture was refluxed for 45 min.Then the mixture was cooled to rt and allyl bromide (720 μL, 8.30 mmol)dissolved in THF (10 mL) was added slowly. The mixture was stirred for4.5 h, then quenched with satd aq NH₄Cl (25 mL) and extracted withether. The combined organic phases were washed with aq NaHCO₃ (5%) andbrine and dried (Na₂SO₄). The solvents were removed under reducedpressure and the residue was crystallized from hexanes and filtered. Thefiltrate was purified by column chromatography (silica, ether/hexanes,1:4), affording a light yellow oil (1.04 g, 59%). IR (neat): {tilde over(v)} 3077, 2955, 2904, 2846, 1639, 1619, 1517; ¹H NMR δ 0.79 (s, 3H),1.29 (s, 3H), 3.38 (d, ³J=6.6 Hz, 2H), 3.64 (d, ²J=11.0 Hz, 2H), 3.76(d, ²J=11.0 Hz, 2H), 5.00-5.10 (m, 2H), 5.37 (s, 1H), 5.86-6.01 (m, 1H),7.19, 7.43 (AA′BB′, 2×2H); ¹³C NMR (APT) δ 21.7 (−), 22.9 (−), 30.0 (+),39.8 (+), 77.5 (+), 101.5 (−), 115.6 (+), 126.1 (−), 128.4 (−), 136.3(+), 137.2 (−), 140.5 (+); GC-MS (EI) obsd 232, 231, 191, 163, 145, 115,105, 91, 69, 56, 41; Anal. Calcd for C₁₅H₂₀O₂: C, 77.55; H, 8.68. Found:C, 77.52; H, 8.77.

2-{4-[3-(S-Acetylthio)propyl]phenyl}-5,5-dimethyl-1,3-dioxane (14)

Following a general procedure (Lub et al. (1997) Liebigs Ann. Recueil,2281-2288), 13 (845 mg, 3.60 mmol) and thioacetic acid (910 μL, 12.7mmol) were dissolved in toluene (20 mL) and the solution was purged withargon for 15 min. Then AIBN (200 mg) was added and the mixture washeated to 90° C. Over a period of 23 h more AIBN (1.10 g) was added inseveral portions. Then aq NaHCO₃ (10%, 50 mL) was added and the phaseswere separated. The aqueous phase was washed with ether and the combinedorganic phases were dried (Na₂SO₄). Purification by columnchromatography (silica, ether/hexanes, 1:4) gave an orange oil, whichsolidified upon standing at −20° C. and was recrystallized from pentaneto give 708 mg (63%) of colorless needles. mp 44° C. IR (neat): {tildeover (v)} 2951, 2850, 1692, 1620, 1518; ¹H NMR δ 0.79 (s, 3H), 1.29 (s,3H), 1.78-1.94 (m, 2H), 2.33 (s, 3H), 2.68 (t, ³J=7.3 Hz, 2H), 2.86 (t,³J=7.3 Hz, 2H), 3.64 (d, ²J=11.0 Hz, 2H), 3.76 (d, ²J=11.0 Hz, 2H), 5.37(s, 1H), 7.18, 7.42 (AA′BB′, 2×2H); ¹³C NMR (APT) δ 21.6 (−), 22.8 (−),28.1 (+), 29.9 (+), 30.4 (−), 30.8 (+), 34.3 (+), 77.3 (+), 101.4 (−),126.0 (−), 128.1 (−), 136.1 (+), 141.5 (+), 195.3 (+); GC-MS (EI) obsd308, 307, 265, 232, 221, 204, 199, 180, 146, 133, 115, 91, 69, 43; Anal.Calcd for C₁₇H₂₄O₃S: C, 66.20; H, 7.84; S, 10.40. Found: C, 66.19; H,7.89; S, 10.54.

4-[3-(S-Acetylthio)propyl]benzaldehyde (15)

Compound 14 (525 mg, 1.70 mmol) was dissolved in CH₂Cl₂ (10 mL) and TFA(2.0 mL) was added together with a drop of water. The solution wasstirred for 15 h at rt. Then aq NaHCO₃ (5%, 35 mL) was added and thephases were separated. The organic phase was washed twice with aq NaHCO₃(5%), once with brine and dried (Na₂SO₄). The solvents were removedunder reduced pressure and the oily residue was purified by columnchromatography (silica, ether/hexanes, 1:2), affording a yellow oil (279mg, 74%). IR (neat): {tilde over (v)} 3037, 2928, 2849, 2731, 1693,1605; ¹H NMR δ 1.88-1.99 (m, 2H), 2.35 (s, 3H), 2.78 (t, ³J=7.3Hz, 2H),2.89 (t, ³J=7.3Hz, 2H), 7.35, 7.81 (AA′BB′, 2×2H), 9.98 (s, 1H); ¹³C NMR(APT) δ 28.1 (+), 30.4 (+), 34.7 (+), 128.8 (−), 129.7 (−), 134.4 (+),148.3 (+), 191.6 (−), 195.2 (+); GC-MS (EI) obsd 222, 180, 146, 133,117, 105, 91, 43.

7-(S-Acetylthio)heptanal (17)

To a solution of crude 7-bromoheptanal (Enders and Bartzen (1991)Liebigs Ann. Chem, 569-574) (3.32 g, 17.2 mmol) in acetone (50 mL) wasadded potassium thioacetate (2.36 g, 21 mmol) under stirring at rt. Thenthe mixture was refluxed, yielding a precipitate after a few minutes.The reaction was monitored by TLC and cooled to rt when no startingmaterial was detectable (4 h). Water (50 mL) was added, the mixture wasextracted with ethyl ether until the organic phase was colorless, andthe combined organic phases were dried (Na₂SO₄) and evaporated.Distillation at 98° C. with a water suction pump afforded 1.66 g (51%,42% from 7-bromoheptanol) of a yellow oil. IR (neat): {tilde over (v)}2938, 2857, 2721, 1725, 1694; ¹H NMR δ 1.28-1.43 (m, 4H), 1.53-1.69 (m,4H), 2.33 (s, 3H), 2.43 (dt, ³J=7.3Hz, ³J=1.5Hz, 2H), 2.86 (t, ³J=7.3Hz, 2H), 9.77 (t, ³J=1.5 Hz, 1H); ¹³C NMR (APT) δ 21.6 (+), 28.1 (+),28.3 (+), 28.6 (+), 29.0 (+), 30.3 (−), 43.3 (+), 195.4 (+), 202.0 (−);GC-MS (EI) obsd 188, 187, 145, 128, 112, 94, 43.

1-[4-(S-acetylthio)phenyl]-2-(diethoxymethyl)acetylene (18)

Samples of 1 (500 mg, 1.80 mmol), CuI (19.0 mg, 100 μmol) andPd(PPh₃)₂Cl₂ (8.4 mg, 12 μmol) were placed in a Schlenk flask. The flaskwas evacuated via vacuum pump for 3 min and then backflushed with argonfor 3 min. The process of evacuation and flushing was repeated 3 times.At this point the argon flow rate was increased and the threadedstopcock was removed. Deareated THF (5.0 mL) and DIEA (5.0 mL) wereadded in succession to the flask by gastight syringe. The threadedstopcock was replaced, the argon flow rate was reduced and the flask wasimmersed in an oil bath thermostated at 40° C. The reaction was stoppedafter 40 h and the mixture was evaporated. The resulting orange-brownsolid was chromatographed (silica, CH₂Cl₂/hexanes, 1:1, then 7:3) toafford a yellowish-white oil (319 mg, 63.8%). ¹H NMR δ 1.27 (t, J=6.6Hz, 6H), 2.40 (s, 3H), 3.5-4.0 (m, 4H), 5.49 (s, 1H), 7.36, 7.50(AA′BB′, 2×2H); ¹³C NMR δ 15.8, 30.9, 61.7, 85.0, 86.8, 92.4, 123.7,129.5, 133.1, 134.8, 193.7; FAB-MS obsd 278.0970, calcd exact mass278.0977; Anal. Calcd. for C₁₅H₁₈O₃S: C, 64.72; H, 6.52; S, 11.52.Found: C, 64.45; H, 6.53; S, 11.34.

5,10,15-trimesityl-20-[4-{2-[4-(S-acetylthio)phenyl]ethynyl}phenyl]porphyrin(19)

Following a general procedure for mixed-aldehyde condensations (Lindseyet al. (1991) Tetrahedron, 50: 8941-8968; Ravikanth et al. (1998)Tetrahedron, 54: 7721-7734) with mesitaldehyde,⁵² aldehyde 4 (204 mg,0.730 mmol) was added to CHCl₃ (40 mL, containing 0.75% ethanol),followed by mesitaldehyde (0.32 mL, 2.2 mmol), pyrrole (200 μL, 2.92mmol) and BF₃.OEt₂ (90 μL, 0.71 mmol). The reaction mixture was stirredat rt for 90 min. Then DDQ (500 mg, 2.20 mmol) in THF (10 mL) was added.The resulting mixture was stirred at rt for 1 h and then passed over ashort silica column (CH₂Cl₂/hexanes, 1:1) affording porphyrins free fromdark pigments and quinone species. The mixture of porphyrins waspurified by preparative centrifugal chromatography (silica,CH₂Cl₂/hexanes, 5:7). The title porphyrin eluted as the second purpleband, affording 78 mg (12%). ¹H NMR δ −2.40 (s, 2H), 1.99 (s, 18H), 2.57(s, 3H), 2.73 (s, 9H), 7.40 (s, 6H), 7.58, 7.61 (AA′BB′, 2×2H), 8.04,8.34 (AA′BB′, 2×2H), 8.78 (s, 4H), 8.8-9.0 (m, 4H); LD-MS obsd 917.2,932.2 [M⁺+15], 890.0 [M⁺ −28], 875.0 [M⁺ —CH₃CO]; FAB-MS obsd 914.4059,calcd exact mass 914.4018 (C₆₃H₅₄N₄OS); λ_(abs) (CH₂Cl₂) 420, 515, 550,592, 646 nm.

5,10,15-Trimesityl-20-[4-{2-[4-(S-acetylthiomethyl)phenyl]ethynyl}phenyl]-porphyrin(20)

Following the general procedure for 19, aldehyde 8 (214 mg, 0.730 mmol),mesitaldehyde (0.32 mL, mmol), pyrrole (200 μL, 2.92 mmol) and BF₃.OEt₂(90 μL, 0.71 mmol) were stirred in CHCl₃ (40 mL) for 1.5 h. Theresulting mixture was treated with DDQ (500 mg, 2.20 mmol) in THF (10mL) for 1 h. Filtration over a silica pad (CH₂Cl₂) followed bypreparative centrifugal chromatography (silica, CH₂Cl₂/hexanes, 5:7)gave the title porphyrin as the second purple band, affording 96 mg(14%). ¹H NMR δ −2.53 (s, 2H), 1.85 (s, 18H), 2.35 (s, 3H), 2.59 (s,9H), 4.13 (s, 2H), 7.26 (s, 6H), 7.31, 7.59 (AA′BB′, 2×2H), 7.90, 8.19(AA′BB′, 2×2H), 8.65 (s, 4H), 8.7-8.9 (m, 4H); LD-MS obsd 932.1, 847.9[M⁺+15], 903.7 [M⁺ −28], 889.5 [M⁺ —CH₃CO], 856.3 [M⁺ —CH₃COS], 841.4[M⁺ —CH₃COSCH₂] FAB-MS obsd 928.4193, calcd exact mass 928.4175(C₆₄H₅₆N₄OS); λ_(abs) (CH₂Cl₂) 420, 515, 548, 592, 648 nm.

5,10,15-Trimesityl-20-[2,3,5,6-tetrafluoro-4-(S-acetylthio)phenyl]porphyrin(21)

Following the general procedure for 19, aldehyde 9 (184 mg, 0.730 mmol),mesitaldehyde (0.32 mL, 2.2 mmol), pyrrole (200 μL, 2.92 mmol) andBF₃.OEt₂ (90 μL, 0.71 mmol) were stirred in CHCl₃ (40 mL) for 1.5 h. Theresulting mixture was treated with DDQ (500 mg, 2.20 mmol) in THF (10mL) for 1 h. Filtration over a silica pad (CH₂Cl₂) followed bypreparative centrifugal chromatography (silica, CH₂Cl₂/hexanes, 1:4)gave the title porphyrin as the second purple band, affording 46 mg(7.1%). ¹H NMR (THF-d₈) δ −2.51 (s, 2H), 1.83 (s, 18H), 2.61 (s, 9H),2.67 (s, 3H), 7.29 (s, 6H), 8.8-9.0 (m, 8H); LD-MS obsd 887.2, 902.2[M⁺+15], 859.0 [M⁺ −28], 845.0 [M⁺ —CH₃CO]; FAB-MS obsd 886.3364, calcdexact mass 886.3328 (C₅₅H₄₆F₄N₄OS); λ_(abs) (CH₂Cl₂) 418, 513, 546, 588,644 nm.

5-[4-(S-Acetylthiomethyl)phenyl]-10,15,20-trimesitylporphyrin (22)

Following the general procedure for 19, aldehyde 10 (148 mg, 0.8 mmol),mesitaldehyde (337 μL, 2.3 mmol), pyrrole (211 μL, 3.0 mmol) andBF₃.OEt₂ (94 μL, 0.70 mmol) were stirred in CHCl₃ (125 mL) for 3 h. Theresulting mixture was treated with DDQ (519 mg, 2.3 mmol) for 1 h. Themixture was then filtered through a pad of silica (CH₂Cl₂) followed bycolumn chromatography (silica, CH₂Cl₂/hexanes, 1:3-1:1). The titlecompound eluted as the second purple band, affording 118 mg (19%) as apurple solid. IR (neat): {tilde over (v)} 3318, 2921, 2861, 1695, 1608,1561; ¹H NMR δ −2.58 (s, 2H), 1.84 (s, 12H), 1.85 (s, 6H, 2.50 (s, 3H),2.63 (s, 9H), 4.46 (s, 2H), 7.27 (s, 6H), 7.65, 8.12 (AA′BB′, 2×2H),8.63 (brs, 4H), 8.67 (d, ³J=5.1 Hz, 2H), 8.77 (d, ³J=5.1 Hz, 2H); LD-MSobsd 844.0 [M⁺+15], 829.0 [M⁺], 786.8 [M⁺ —COCH₃], 753.8 [M⁺ —SCOCH₃];FAB-MS obsd 828.3892, calcd exact mass 828.3862 (C₅₆H₅₂N₄OS); λ_(abs)(toluene) 420, 515, 548, 592, 649 nm.

5-{4-[2-(S-Acetylthio)ethyl]phenyl}-10,15,20-trimesitylporphyrin (23)

Following the general procedure for 19, aldehyde 11 (98 mg, 0.5 mmol),mesitaldehyde (208 μL, 1.4 mmol), pyrrole (131 μL, 1.9 mmol) andBF₃.OEt₂ (52 μL, 0.4 mmol) were stirred in CHCl₃ (100 mL) for 3 h. Theresulting mixture was treated with DDQ (320 mg, 1.4 mmol) for 1.5 h. Themixture was then filtered through a pad of silica (CH₂Cl₂) followed bycolumn chromatography (silica, CH₂Cl₂/hexanes, 1:1-3:2). The titlecompound comprised the second purple band, affording 69 mg (17%) as apurple solid. IR (neat): {tilde over (v)} 3319, 2920, 2861, 1694, 1608,1561; ¹H NMR δ −2.57 (s, 2H), 1.85 (s, 18H), 2.45 (s, 3H), 2.62 (s, 9H),3.21 (t, ³J=8.1 Hz, 2H), 3.37-3.52 (m, 2H), 7.27 (s, 2H), 7.27 (s, 6H),7.58, 8.13 (AA′BB′, 2×2H), 8.62 (s, 4H), 8.67 (d, ³J=5.1 Hz, 2H), 8.77(d, ³J=4.4 Hz, 2H); LD-MS obsd 860.4 [M⁺+15], 845.3 [M⁺], 803.1 [M⁺—COCH₃], 769.0 [M⁺ —SCOCH₃]; FAB-MS obsd 842.4025, calcd exact mass842.4018 (C₅₇H₅₄N₄OS); λ_(abs) (toluene) 420, 515, 548, 593, 650 nm.

5-{4-[3-(S-Acetylthio)propyl]phenyl}-10,15,20-trimesitylporphyrin (24)

Following the general procedure for 19, aldehyde 15 (108 mg, 0.5 mmol),mesitaldehyde (215 μL, 1.5 mmol), pyrrole (135 μL, 1.9 mmol) andBF₃.OEt₂ (54 μL, 0.4 mmol) were stirred in CHCl₃ (100 mL) for 3.5 h. Theresulting mixture was treated with DDQ (331 mg, 1.5 mmol) for 1 h. Themixture was then filtered through a pad of silica (CH₂Cl₂) followed bycolumn chromatography (silica, CH₂Cl₂/hexanes 3:2-2:1). The titlecompound comprised the second purple band as a purple solid, which wasrecrystallized from methanol to afford 41 mg (48 μL, 10%) of a purplesolid. IR (neat): {tilde over (v)} 3322, 3102, 2920, 2852, 1693, 1612,1559; ¹H NMR: δ −2.56 (s, 2H), 1.85 (s, 18H), 2.14-2.25 (m, 2H), 2.41(s, 3H), 2.61 (s, 9H), 3.02 (t, ³J=7.3 Hz, 2H), 3.37 (t, ³J=7.3 Hz, 2H),8.79 (d, ³J=4.4 Hz, 7.53, 8.11 (AA′BB′, 2×2H), 8.63 (s, 4H), 8.67 (d,³J=4.4 Hz, 2H), 8.79 (d, ³J=4.4 Hz, 2H); LD-MS obsd 873.4 [M⁺+15], 858.4[M⁺], 816.2 [M⁺ —COCH₃]; FAB-MS obsd 856.4216, calcd exact mass 856.4175(C₅₈H₅₆N₄OS); λ_(abs) (toluene) 420, 515, 548, 593, 649 nm.

5-[7-(S-Acetylthio)hexyl]-10,15,20-trimesitylporphyrin (25)

Following the general procedure for 19, aldehyde 17 (111 mg, 0.6 mmol),mesitaldehyde (261 μL, 1.8 mmol), pyrrole (164 μL, 2.4 mmol) andBF₃.OEt₂ (65 μL, 0.5 mmol) were stirred in CHCl₃ (100 mL) for 3 h. Theresulting mixture was treated with DDQ (401 mg, 1.8 mmol) for 1.5 h. Themixture was then filtered through a pad of silica (CH₂Cl₂) followed bytwo column chromatography procedures (silica, CH₂Cl₂/hexanes, 1:1-3:2).The title compound eluted as the second purple band and was purified bycolumn chromatography (silica, CH₂Cl₂/hexanes, 2:1) to afford 105 mg(22%) as a purple solid. IR (neat): {tilde over (v)} 3317, 3107, 2922,2856, 1691, 1609, 1562; ¹H NMR δ −2.51 (s, 2H), 1.52-1.67 (m, 4H),1.74-1.89 (m, 2H), 1.85 (s, 18H), 2.30 (s, 3H), 2.45-2.58 (m, 2H), 2.60(s, 3H), 2.63 (s, 6H), 2.88 (t, ³J=6.6 Hz, 2H), 4.98 (t, ³J=8.1 Hz, 2H),7.25 (s, 2H), 7.28 (s, 4H), 8.55-8.62 (m, 4H), 8.75 (d, ³J=3.7 Hz, 2H),8.40 (d, 2H, ³J=3.7 Hz); LD-MS obsd 825.2 [M⁺], 783.0 [M⁺ —COCH₃], 679.5[M⁺ —(CH₂)₅SCOCH₃]; FAB-MS obsd 822.4355, calcd exact mass 822.4331(C₅₅H₅₈N₄OS); λ_(abs) (toluene) 419, 516, 549, 594, 652 nm.

5,10,15-Trimesityl-20-{2-[4-(S-acetylthio)phenyl]ethynyl}porphyrin (26)

Following the general procedure for 19, acetal 18 (100 mg, 0.36 mmol),mesitaldehyde (0.16 mL, mmol), pyrrole (100 μL, 1.46 mmol) and BF₃.OEt₂(45 μL, 0.35 mmol) were stirred in CHCl₃ (20 mL) for 1.5 h. Theresulting mixture was treated with DDQ (250 mg, 1.10 mmol) in THF (5 mL)for 1 h. Filtration over a silica pad (CH₂Cl₂) followed by twosubsequent preparative centrifugal chromatography (silica,CH₂Cl₂/hexanes, 1:3, then 1:1) gave the title porphyrin as the secondpurple band, affording 2.5 mg (0.83%). ¹H NMR δ −2.14 (s, 2H), 1.85 (s,18H), 2.50 (s, 3H), 2.63 (s, 9H), 7.25 (s, 6H), 7.60, 8.03 (AA′BB′,2×2H), 8.54 (s, 4H), 8.73 (m, 2H), 9.63 (m, 2H); LD-MS obsd 841.6, 856.6[M⁺+15], 813.4 [M⁺−28], 799.4 [M⁺ —CH₃CO]; FAB-MS obsd 838.3737, calcdexact mass 838.3705 (C₅₇H₅₀N₄OS); λ_(abs) (CH₂Cl₂) 436, 534, 576, 611,668 nm.

General Procedure for Zinc Insertion

The porphyrin was dissolved in CHCl₃ or CH₂Cl₂ and a solution ofZn(OAc)₂.2H₂O in methanol was added. The reaction mixture was stirred atrt. After metalation was complete (TLC, fluorescence excitationspectroscopy), the reaction mixture was washed with water and dried(Na₂SO₄), filtered and concentrated to a purple solid. Purification wasachieved by column chromatography on silica.

Zn(II)-5,10,15-Trimesityl-20-[4-{2-[4-(S-acetylthio)phenyl]ethynyl}phenyl]-porphyrin(Zn-19)

A solution of porphyrin 19 (37 mg, 0.040 mmol) in CH₂Cl₂ (15 mL) wastreated with Zn(OAc)₂.2H₂O (880 mg, 4.00 mmol) in MeOH (15 mL) and themixture was stirred for 16 h. Column chromatography (silica,CH₂Cl₂/hexanes, 1:1) afforded 35.6 mg (92.0%). ¹H NMR δ 1.85 (s, 18H),2.48 (s, 3H), 2.64 (s, 9H), 7.27 (s, 6H), 7.48, 7.72 (AA′BB′, 2×2H),7.92, 8.23 (AA′BB′, 2×2H), 8.70 (s, 4H), 8.70-8.90 (m, 4H); LD-MS obsd979.8, 995.8 [M⁺+15], 953.6 [M⁺−28], 939.6 [M⁺ —CH₃CO]; FAB-MS obsd976.3177, calcd exact mass 976.3153 (C₆₃H₅₂N₄OSZn); λ_(abs) (CH₂Cl₂)422, 550 nm.

Zn(II)-5,10,15-Trimesityl-20-[4-{2-[4-(S-acetylthiomethyl)phenyl]ethynyl}phenyl]porphyrin(Zn-20)

A solution of porphyrin 20 (37 mg, 0.040 mmol) in CH₂Cl₂ (15 mL) wastreated with Zn(OAc)₂.2H₂O (880 mg, 4.00 mmol) in MeOH (15 mL) and themixture was stirred for 16 h. Column chromatography (silica,CH₂Cl₂/hexanes, 1:1) afforded 37.7 mg (95.0%). ¹H NMR (THF-d₈) δ 1.86(s, 18H), 2.34 (s, 3H), 2.60 (s, 9H), 4.18 (s, 2H), 7.29 (s, 6H), 7.38,7.58 (AA′BB′, 2×2H), 7.88, 8.19 (AA′BB′, 2×2H), 8.63 (s, 4H), 8.6-8.8(m, 4H); LD-MS obsd 992.4, 1008.5 [M⁺+15], 964.4 [M⁺−28], 950.2 [M⁺—CH₃CO], 934.2 [M⁺−58], 918.1 [M⁺ —CH₃COS], FAB-MS obsd 990.3280, calcdexact mass 990.3310 (C₆₄H₅₆N₄OS); λ_(abs) (CH₂Cl₂) 422, 550 nm.

Zn(II)-5,10,15-Trimesityl-20-[2,3,5,6-tetrafluoro-4-(S-acetylthio)phenyl]porphyrin(Zn-21)

A solution of porphyrin 21 (35 mg, 0.040 mmol) in CH₂Cl₂ (15 mL) wastreated with Zn(OAc)₂.2H₂O (880 mg, 4.00 mmol) in MeOH (15 mL) and themixture was stirred for 16 h. Column chromatography (silica,CH₂Cl₂/hexanes, 1:4) afforded 31.4 mg (83.3%). ¹H NMR (THF-d₈) δ 1.87(s, 18H), 2.66 (s, 9H), 2.71 (s, 3H), 7.30 (s, 6H), 8.7-9.0 (m, 8H);LD-MS obsd 953.5, 967.7 [M⁺+15], 925.4 [M⁺−28], 909.3 [M⁺ —CH₃CO];FAB-MS obsd 948.2480, calcd exact mass 948.2463 (C₅₅H₄₄F₄N₄OSZn);λ_(abs) (CH₂Cl₂) 421, 548 nm.

Zn(II)-5-[4-(S-Acetylthiomethyl)phenyl]-10,15,20-trimesitylporphyrin(Zn-22)

A solution of porphyrin 22 (54.8 mg, 66.1 μmol) in CHCl₃ (20 mL) wastreated with Zn(OAc)₂.2H₂O (435 mg, 2.00 mmol) in MeOH (5 mL) and themixture was stirred for 6 h. An excess of Zn(OAc)₂.2H₂O (290 mg, 1.3mmol) was added because the metalation was not completed. Stirring wascontinued for another 23 h. The organic phase was washed with aq NaHCO₃(5%). Column chromatography (silica, CH₂Cl₂/hexanes, 1:1) afforded apurple solid in quantitative yield. IR (neat): {tilde over (v)} 2922,2853, 1663; ¹H NMR δ 1.84 (s, 18H), 2.49 (s, 3H), 2.63 (s, 9H), 4.46 (s,2H), 7.27 (s, 6H), 7.63, 8.14 (AA′,BB′, 2×2H), 8.70 (brs, 4H), 8.74 (d,³J=4.4 Hz, 1H), 8.75 (d, ³J=4.4 Hz, 1H), 8.845 (d, ³J=4.4 Hz, 1H), 8.850(d, ³J=4.4 Hz, 1H); LD-MS obsd 906.3 [M⁺+15], 891.3 [M⁺], 849.2 [M⁺—COCH₃], 831.2 [M⁺-4CH₃], 816.1 [M⁺ —SCOCH₃]; FAB-MS obsd 890.3035,calcd exact mass 890.2997 (C₅₆H₅₀N₄OSZn); λ_(abs) (toluene) 423, 550 nm;λ_(em) (toluene) 593, 644 nm.

Zn(II)-5-{4-[2-(S-Acetylthio)ethyl]phenyl}-10,15,20-trimesitylporphyrin(Zn-23)

A solution of porphyrin 23 (48 mg, 57 μmol) in CHCl₃ (20 mL) was treatedwith Zn(OAc)₂.2H₂O (1.25 g, 5.70 mmol) in MeOH (5 mL) and the mixturewas stirred for 17 h. The organic phase was washed with aq NaHCO₃ (5%).Column chromatography (silica, CH₂Cl₂/hexanes, 3:1) afforded a purplesolid in quantitative yield. IR (neat): {tilde over (v)} 3096, 2910,2849, 1646; ¹H NMR δ 1.84 (s, 12H), 1.85 (s, 6H), 2.44 (s, 3H), 2.63 (s,9H), 3.20 (t, ³J=7.3 Hz, 2H), 3.38-3.46 (m, 2H), 7.27 (s, 6H), 7.57,8.14 (AA′BB′, 2×2H), 8.70 (s, 4H), 8.75 (d, ³J=4.4 Hz, 2H), 8.86 (d,³J=4.4 Hz, 2H); LD-MS obsd 920.5 [M⁺+15], 906.4 [M⁺], 864.3 [M⁺ —COCH₃],830.2 [M⁺ —SCOCH₃]; FAB-MS obsd 904.3121, calcd exact mass 904.3153(C₅₇H₅₂N₄OSZn); λ_(abs) (toluene) 423, 550 nm; λ_(em) (toluene) 593, 644nm.

Zn(II)-5-{4-[3-(S-Acetylthio)propyl]phenyl}-10,15,20-trimesitylporphyrin(Zn-24)

A solution of porphyrin 24 (37.7 mg, 44 μmol) in CHCl₃ (20 mL) wastreated with Zn(OAc)₂.2H₂O (965 mg, 4.40 mmol) in MeOH (5 mL) and themixture was stirred for 5 h. The organic phase was washed with aq NaHCO₃(5%) and dried (Na₂SO₄). Column chromatography (silica, CH₂Cl₂/hexanes,4:1) afforded a purple solid in quantitative yield. IR (neat): {tildeover (v)} 3107, 2919, 2849, 1650; ¹H NMR δ 1.84 (s, 12H), 1.85 (s, 6H),2.13-2.26 (m, 2H), 2.40 (s, 3H), 2.63 (s, 9H), 3.03 (t, ³J=7.3 Hz, 2H),3.11 (t, ³J=7.3 Hz, 2H), 7.27 (s, 6H), 7.53, 8.13 (AA′BB′, 2×2H), 8.69(s, 4H), 8.74 (d, ³J=5.1 Hz, 2H), 8.86 (d, ³J=5.1 Hz, 2H); LD-MS obsd937.8 [M⁺+15], 921.8 [M⁺], 879.6 [M⁺ —COCH₃]; FAB-MS obsd 918.3343,calcd exact mass 918.3310 (C₅₈H₅₄N₄OSZn); λ_(abs) (toluene) 423, 550 nm;λ_(em) (toluene) 593, 644 nm.

Zn(II)-5-[7-(S-Acetylthio)hexyl]-10,15,20-trimesitylporphyrin (Zn-25)

A solution of porphyrin 25 (93 mg, 110 μmol) in CHCl₃ (25 mL) wastreated with Zn(OAc)₂.2H₂O (2.50 g, 11.4 mmol) in MeOH (7 mL) and themixture was stirred for 18 h. The organic phase was washed with aqNaHCO₃ (5%) and dried (Na₂SO₄). Column chromatography (silica,CH₂Cl₂/hexanes, 2:1) afforded a purple solid (85 mg) in 85% yield. IR(neat): {tilde over (v)} 3107, 2920, 2849, 1690, 1658, 1608; ¹H NMR δ1.55-1.67 (m, 4H), 1.78-1.89 (m, 2H), 1.83 (s, 18H), 2.20 (s, 3H),2.52-2.65 (m, 2H), 2.61 (s, 3H), 2.64 (s, 6H), 2.83 (t, ³J=6.6 Hz, 2H),5.02 (t, ³J=8.1 Hz, 2H), 7.25 (s, 2H), 7.28 (s, 4H), 8.64 (d, ³J=5.1 Hz,2H), 8.66 (d, ³J=5.1 Hz, 2H), 8.81 (d, ³J=4.4 Hz, 2H), 9.49 (d, ³J=4.4Hz, 2H); LD-MS obsd 887.7 [M⁺], 844.5 [M⁺ —COCH₃], 742.0[M⁺-(CH₂)₅SCOCH₃]; FAB-MS obsd 884.3490, calcd exact mass 884.3466(C₅₅H₅₆N₄OSZn); λ_(abs) (toluene) 423, 552 nm; λ_(em) (toluene) 593, 646nm.

Zn(II)-5,10,15-Trimesityl-20-{2-[4-(S-acetylthio)phenyl]ethynyl}porphyrin(Zn-26)

A solution of porphyrin 26 (2.5 mg, 2.9 μmol) in CH₂Cl₂ (5 mL) wastreated with Zn(OAc)₂.2H₂O (64 mg, 29 μmol) in MeOH (5 mL) and themixture was stirred for 16 h. Column chromatography (silica,CH₂Cl₂/hexanes, 1:1) afforded 2.4 mg (92%). ¹H NMR δ 1.85 (s, 18H), 2.50(s, 3H), 2.62 (s, 9H), 7.29 (s, 6H), 7.60, 8.04 (AA′BB′, 2×2H), 8.64 (m,4H), 8.82 (m, 2H), 9.73 (m, 2H); LD-MS obsd 906.1, 922.1 [M⁺+15], 878.4[M⁺−28], 862.0 [M⁺ —CH₃CO]; FAB-MS obsd 900.2825, calcd exact mass900.2840 (C₅₇H₄₈N₄OSZn); λ_(abs) (CH₂Cl₂) 440, 566, 611 nm.

Electrochemistry

The solution electrochemical studies of the Zn porphyrins were performedusing techniques and instrumentation previously described (Seth et al.(1994) J. Am. Chem. Soc., 116: 10578-10592; Seth et al.(1996) J. Am.Chem. Soc., 118: 11194-11207). The solvent was CH₂Cl₂;tetrabutylammonium hexafluorophosphate (TBAH, 0.1 M) (Aldrich,recrystallized three times from methanol and dried under vacuum at 110°C.) served as supporting electrolyte. The potentials reported are vsAg/Ag⁺; E_(1/2)(FeCP₂/FeCP₂ ⁺)=0.19 V.

The SAM electrochemical studies of the Zn porphyrins were performed on75-micron wide gold band electrodes formed via E-beam evaporation (to athickness of 100 nm) onto piranha-solution-etched glass slides that hada 1 nm thick underlayer of chromium. The electrochemical cell wasconstructed by forming a 3-mm diameter polydimethylsiloxane (PDMS) well(˜3 mm deep) over the gold band. The Zn porphyrins were dissolved inabsolute ethanol and the solution (˜1 mM) was added to the well andallowed to stand. Deposition times of 30 min were found to give the samequality cyclic voltammograms as those obtained with much longerdeposition times (12 h). Subsequent to soaking, the solvent was removedand the PDMS well was rinsed with absolute ethanol followed by a finalrise with CH₂Cl₂. A small amount of CH₂Cl₂ containing 1 M TBAH was thenadded to the PDMS well. Silver and platinum wires were inserted into thewell to serve as the reference and counter electrodes, respectively. Thecyclic voltammograms were recorded with an Ensman Instruments 400potentiostat at a rate of 100 V/s.

Example 5 Synthesis of Thiol-Derivatized Ferrocenes andThiol-Derivatized Ferrocene-Porphyrins for Comparative Studies ofMolecular-Based Information Storage

This example describes the systhesis of various ferrocene-porphyrins.Three of the ferrocene-porphyrins have linkers of different lengthbetween the ferrocene and porphyrin. The fourth ferrocene-porphyrin hastwo ferrocenes positioned at the lateral sites on the porphyrin. Thelatter architecture is designed to provide a shorter distance betweenthe electroactive surface and the ferrocene while maintaining an uprightorientation of the porphyrin. Each ferrocene-porphyrin affords threecationic oxidation states (ferrocene monocation, porphyrin monocation,porphyrin dication) in addition to the neutral state thereby affordingthe capability of storing two bits of information. Each ferrocene orferrocene-porphyrin bears an S-acetyl or S—(N-ethyl)carbamoyl protectedthiol moiety, thereby avoiding handling of free thiols. Eachferrocene-porphyrin forms a self-assembled monolayer (SAM) on gold viain situ cleavage of the thiol protecting group. The SAMs of all arraysare electrochemically robust and exhibit three well-resolved, reversibleoxidation waves.

Introduction.

We have shown that a self-assembled monolayer (SAM) of porphyrinsattached to an electroactive surface can be used for molecular-basedinformation storage. The porphyrins are addressed electrically andinformation is stored in the distinct oxidation states provided by theporphyrins. In principle, multiple bits of information can be stored ina given memory storage location (i.e., a memory cell) by accessing aseries of distinct oxidation states of a molecular assembly. Gold, theelectroactive surface predominantly employed, presents anelectrochemical window that extends to ˜+1.2 V (versus Ag/Ag⁺). A numberof writing and reading schemes require a potential difference of ΔE=150mV in order to distinguish distinct oxidation states. Thus, to storemultiple bits it is useful to have redox-active molecules that span thefull potential provided by the gold electrode. For purposes of stabilitywe have selected redox-active molecules that are reversibly cycledbetween neutral and cationic states rather than anionic states, giventhe greater stability of cations under ambient conditions.

We have described herein the synthesis of thiol-derivatized porphyrinsfor attachment to electroactive surfaces. Porphyrins have two stable andeasily accessible cationic oxidation states (monocation, dication)(Felton (1978) In The Porphyrins; Dolphin, D., Ed.; Academic Press, N.Y.5: 53-126). In porphyrins the electrochemical potentials can be tuned byattachment of appropriate substituents (Yang et al., (1999) J.Porphyrins Phthalocyanines 3: 117-147) or by variation in the centralmetal (Fuhrhop, et al. (1969) Am. Chem. Soc, 91: 4174-4181), therebyachieving oxidation potentials in the range of +0.5-+1.2 V.

In optimizing storage molecules according to the present invention, wehave explored a number questions such as Whether, or not, there is adifference between co-depositing a collection of different types ofmolecules having distinct oxidation potentials in a memory storagelocation, versus employing a homogeneous population of molecules whereeach molecule is comprised of multiple redox-active units. The formerapproach is more easily implemented while the latter avoids potentialproblems such as differential partitioning onto the surface and/orcompartmentalization of attached molecules that may occur with aheterogeneous population of molecules. We have aslo explored how therate of electron transfer (and therefore the rate of writing andreading) and memory persistence lifetime are affected by moleculararchitecture? In addition, we have explored the effects of linker lengthand composition on rate of electron transfer of redox-active moleculesattached to SAMs.

One of the most widely studied redox-active molecules in self-assembledmonolayers (SAMs) is ferrocene (Chidsey (1991) Science, 251: 919-921;Tender et al., (1994) Anal. Chem. 66: 3173-3178; Weber et al. (1994)Anal. Chem. 66: 3164-3168; Everett, et al. (1995) Anal. Chem., 67:292-298; Campbell et al. (1996) J. Am. Chem. Soc., 118: 10211-10219;Sachs et al. (1997) J. Am. Chem. Soc., 119: 10563-10564; Creager et al.,(1999) J. Am. Chem. Soc. 121: 1059-1064; Kondo et al., (1999) J. Am.Chem. Soc., 121: 391-398; Ye et al, (1999) Phys. Chem. Chem. Phys., 1:3653-3659), due to the central role played by ferrocene in non-aqueouselectrochemical studies. Ferrocenes present a number of attractiveelectrochemical features. Ferrocenes exhibit relatively stable radicalcations. The electrochemical potential can be tuned by attachment ofappropriate substituents (and other metallocenes can be employed),affording oxidation potentials in the range of −0.2 to >+0.5 V(Encyclopedia of Electrochemistry of the Elements, Bard, A. J.; Lund,H.; Eds.; Marcel Dekker: New York, 1979, Vol. 13, pp 3-27). One keydistinction between a ferrocene and a porphyrin, however, is thatferrocene only has two easily accessible oxidation states (neutral,monocation), while porphyrins have three accessible and stable oxidationstates (neutral, monocation, dication). The distinct electrochemicalwindows that are readily accessible with ferrocenes and porphyrinsprompted us to explore the combination of porphyrins and ferrocenes inorder to span the electrochemical window provided on a gold surface.

Thiol-derivatized ferrocene-porphyrins are attractive as prototypicalmolecular arrays comprised of multiple redox-active units for studies ofmulti-bit information storage. A large number of ferrocene-porphyrinshave been prepared to date (Uosaki et al. (1997) J. Am. Chem. Soc., 119:8367-8368; Yanagida et al. (1998) Bull. Chem. Soc. Jpn., 71: 2555-2559;Kondo, et al. (1999) Z. Phys. Chem., 212: 23-30; Thornton et al. (1998)J. Phys. Chem. B, 102,:2101-21 10; Beer et al. (1987) J. Organomet.Chem., 336: C17-C21; Beer et al. (1989) J. Organomet. Chem., 366: C6-C8;Wagner et al.,(1991) J. Chem. Soc. Chem. Commun. 1463-1466; Wagner, etal. (1997) Tetrahedron, 53: 6755-6790; Hisatome et al. (1985)Tetrahedron Lett., 26: 2347-2350; Beer et al. (1995) J. Chem. Soc. Chem.Commun., 1187-1189; Beer et al. (1997) J. Chem. Soc. Dalton Trans.881-886; Fujitsuka et al., Chem. Lett. 1999, 721-722; Imahori et al.(1999) Chem. Commun., 1165-1166; Wollmann et al. (1977) Inorg. Chem.,16: 3079-3089; Maiya et al. (1989) Inorg. Chem. 28: 2524-2527; Loim etal. (1996) Mendeleev Commun., 2: 46-47; Loim et al. (1997) Russ. Chem.B., 46: 1193-1194; Loim et al. (1998) Russ. Chem. B., 47, 1016-1020;Boyd et al. (1999) Chem. Commun., 637-638; Nadtochenko et al. (1999)Russ. Chem. B., 48: 1900-1903; Vaijayanthimala et al. (1990) J. Coord.Chem., 21(Part A), 333-342; Schmidt et al. (1986) Inorg. Chem., 25:3718-3720; Giasson, et al. (1993) J. Phys. Chem., 97: 2596-2601; Burrellet al. (1997) Tetrahedron Lett., 38: 1249-1252; Burrell et al. (1999) J.Chem. Soc. Dalton Trans., 3349-3354). The type of linker between the twoelectroactive units in these structures ranges from non-conjugated ether(Uosaki (1997) et al., J. Am. Chem. Soc., 119: 8367-8368; Yanagida etal. (1998) Bull. Chem. Soc. Jpn., 71: 2555-2559; Kondo et al., (1999) Z.Phys. Chem., 212: 23-30; Thornton et al. (1998) J. Phys. Chem. B., 102:2101-2110), ester (Beer et al., (1987) J. Organomet. Chem., 336:C17-C21; Beer et al. (1989) J. Organomet. Chem., 366: C6-C8; Wagner etal., (1991) J. Chem. Soc. Chem. Commun. 1463-1466; Wagner et al. (1997)Tetrahedron, 53: 6755-6790), amide (Hisatome et al. (1985) TetrahedronLett. 26: 2347-2350; Beer et al. (1995) J. Chem. Soc. Chem. Commun.1187-1189; Beer et al. (1997) J. Chem. Soc. Dalton Trans., 881-886;Fujitsuka et al. (1999) Chem. Lett., 721-722; Imahori et al. (1999)Chem. Commun 1165-1166) to conjugated (direct linkage [Wollmann et al.,(1977) Inorg. Chem. 16: 3079-3089; Maiya et al. (1989) Inorg. Chem., 28:2524-2527; Loim et al. (1996) Mendeleev Commun., 2: 46-47; Loim et al.,(1997) Russ. Chem. B., 46: 1193-1194; Loim et al. (1998) Russ. Chem. B.,47: 1016-1020; Boyd et al., (1999) Chem. Commun., 637-638; Nadtochenkoet al. (1999) Russ. Chem. B., 48: 1900-1903), imine (Vaijayanthimala etal. (1990) J. Coord. Chem., 21(Part A): 333-342), phenyl (Schmidt et al.(1986) Inorg. Chem., 25: 3718-3720), alkene (Giasson et al. (1993) J.Phys. Chem., 97: 2596-2601; Burrell et al. (1997) Tetrahedron Lett., 38:1249-1252; Burrell, et al. (1999) J. Chem. Soc. Dalton Trans.,3349-3354). Two ferrocene porphyrins that bear a thiol unit attached tothe end of a long flexible hydrocarbon chain have been prepared forattachment to a gold electrode (Uosaki et al. (1997) J. Am. Chem. Soc.,119: 8367-8368; Yanagida et al. (1998) Bull. Chem. Soc. Jpn., 71:2555-2559; Kondo et al. (1999) Z. Phys. Chem., 212: 23-30; Imahori etal. (1999) Chem. Commun., 1165-1166). For our studies we used a set ofmolecules with a high level of architectural rigidity and appropriatepositioning of ferrocene, porphyrin, linkers, and thiol unit.

In this example, we describe a set of four thiol-derivatized ferroceneporphyrins. In order to achieve a high degree of 3-dimensional order,the p-phenylene linker has been used for attachment of the porphyrin tothe thiol group. Three of the ferrocene-porphyrins are designed suchthat the ferrocene and porphyrin are separated by linkers of differentlength. Each ferrocene-porphyrin is designed for vertical orientationupon binding of the thio group on a gold surface, thereby disposing theferrocene far from the gold surface (Zn-34, Zn-35 and Zn-36). A fourthferrocene-porphyrin explores a different architecture, where theferrocenes are attached to the lateral positions of the porphyrin(Zn-37). In this case the through-bond distance from thiol to ferroceneremains the same as with the ferrocene-porphyrin having the same spacerbut in an upright position (Zn-35) while the through-space distance tothe gold surface is much shorter. This set of ferrocene-porphyrinsshould provide valuable guidance concerning the design of moleculardevices for the storage of multiple bits of information. Two sets offerrocenes with thiol linkers of different lengths and extent ofconjugation also have been synthesized. These thiol-derivatizedferrocene molecules serve as benchmarks for comparison with theferrocene-porphyrins, with the thiol-derivatized porphyrins bearingdiverse linkers described in the previous paper [Gryko, D. T., et al.,submitted, companion paper 1], and with the large body of data wherethiol-derivatized ferrocenes have been attached to electroactivesurfaces. All of the thiol-derivatized molecules are prepared withS-acetyl or S—(N-ethylcarbamoyl) protected thiol groups, which undergoin situ cleavage on a gold electrode and thereby obviate handling offree thiols (Tour et al. (1995) J. Am. Chem. Soc., 117: 9529-9534; Grykoet al. (1999) J. Org. Chem., 64: 8635-8647).

Results and Discussion

Ferrocene-Linked Thiols and Ferrocene Building Blocks

We sought to prepare thiol-derivatized ferrocenes bearing a variety ofaryl or alkyl linkers. Ferrocene is known to undergo arylation with avariety of diazonium salts (Nesmeyanov et al. (1954) Dokl. Akad. NaukS.S.S.R, 97: 459-462; Broadhead et al., (1955) J. Chem. Soc., 367-370;Weinmayr (1955) Am. Chem. Soc., 77: 3012-3014), which is an approach weemployed in the preparation of several of the ferrocene derivatives.Treatment of ferrocene with one molar equivalent of the diazonium saltof 4-iodoaniline afforded 4-iodophenylferrocene (1) in 30% yield (Scheme1, FIG. 48). However, an excess of 4-iodoaniline (3 mol equiv) afforded1 in 55% yield after separation from unreacted ferrocene. Lithiation of4-iodophenylferrocene (1), following by trapping with sulfur (Jones etal. (1970) Org. Syn., 50: 104) and acetyl chloride (Pearson et al.(1997) J. Org. Chem., 62: 1376-1387) at −78° C. gave4-(S-acetylthio)phenylferrocene (2) in 85% yield.

4-{2-[4-(S-acetylthio)phenyl]ethynyl}phenylferrocene (5) was synthesizedby two routes. The first route employed the key intermediate4-[2-(trimethylsilyl)ethynyl]-phenylferrocene (3), which was accessed intwo ways (Scheme 2, FIG. 49). The Pd-coupling (Takahashi et al. (1980)Synthesis, 8: 627-630) of 4-iodophenylferrocene (1) and(trimethylsilyl)acetylene in TEA at 40° C. for 4 h afforded 3.Alternatively, Pd-coupling of 4-iodoaniline with(trimethylsilyl)acetylene gave 4-[2-(trimethylsilyl)ethynyl]aniline(Id.), which upon diazotization and reaction with ferrocene gave 3. Inboth cases 3 was obtained in 50-55% yield. Cleavage of thetrimethylsilyl group in 3 using K₂CO₃ in THF/MeOH gave4-ethynylphenylferrocene (previously synthesized using a less efficientprocedure (Simionescu et al. (1976) J. Organomet. Chem., 113, 23-28)(4), which upon Pd-coupling with 1-iodo-4-(S-acetylthio)benzene in thepresence of TEA gave the desired ferrocene 5 in 56% yield. However, theyield of 5 was greatly improved (88%) with use of DIEA instead of TEAwhich is often used in such Pd coupling reactions.

In the second route to 5, 4-iodo-1-[2-(trimethylsilyl)ethynyl]benzene(Moore et al. (1991) Tetrahedron Lett., 32: 2465-2466; Lavastre et al.(1996) Tetrahedron, 52: 5495-5504; Hsung et al. (1995) Organometal, 14:4808-4815; Yao et al. (1999) J. Org. Chem., 64: 1968-1971) (6) served asa key intermediate. This bifunctional compound has been preparedpreviously for use in the synthesis of molecular nanostructures. Weinvestigated two paths as potential refinements to this key buildingblock (Scheme 2, FIG. 49). Employing Tour's procedure (Yao et al (1990)J. Org. Chem., 64: 1968-1971) but with an improved Pd reagent and amine,the reaction of 1,4-diiodobenzene with 0.5 equiv of(trimethylsilyl)acetylene in TEA at 50° C. for 4 h afforded 6.Alternatively, treatment of the diazonium salt of4-[2-(trimethylsilyl)ethynyl]aniline with KI also afforded 6. Lithiationof 6 and trapping with sulfur and acetyl chloride at −78° C. afforded1-(S-acetylthio)-4-[2-(trimethylsilyl)ethynyl]benzene (7) in 90% yield.Deprotection of 7 with tetrabutylammonium fluoride in the presence ofacetic acid and acetic anhydride following a reported procedure (Pearsonet al (1997) J. Org. Chem., 62: 1376-1387) gave1-(S-acetylthio)-4-ethynylbenzene (8) in 90% yield. Finally, thePd-coupling of 4-iodophenylferrocene (1) and 8 in THF at roomtemperature in the presence of DIEA gave the desired ferrocene 5 in 90%yield.

Although the next target molecule 11 was available (Hsung et al. (1995)Organometal, 14: 4808-4815) via Pd-coupling of ethynylferrocene and1-iodo-4-(S-acetylthio)benzene, we decided to examine another syntheticroute. A slight modification of the catalyst in the Pd-coupling ofethynylferrocene 9 (Doisneau et al. (1992) J. Organomet. Chem, 425:113-117) with excess 1,4-diiodobenzene increased the yield ofintermediate 10 from 73% (Yu et al. (1999) J. Org. Chem., 64: 2070-2079)to 95% (Scheme 3, FIG. 50). Lithiation of 10 following by trapping withelemental sulfur and acetyl chloride at −78° C. afforded the desiredproduct 11 in 95% yield.

We also sought to investigate thiol-derivatized ferrocenes with loweroxidation potentials. Selective reduction of 1,1′-diacetylferrocene to1-ethyl-1′-acetylferrocene 12 has been accomplished using systems suchas H₂/PtO₂ (Rosenblum et al. (1958) J. Am. Chem. Soc., 80: 5443-5448) orZn/Me₃SiCl (Denifil et al. (1996) J. Organomet. Chem., 523: 79-91)albeit in modest yield. Thus, we decided to apply the classicalClemmensen system (Zn/HgCl₂ amalgam and HCl), which gave 12 in up to 60%yield (Scheme 4, FIG. 51). The same sequence of reactions employed toprepare 11 was then applied to 12. In this manner, 12 was converted intothe ethynylferrocene 13, which was coupled with 1,4-diiodobenzene togive 14, and the latter was treated with t-BuLi, sulfur, and acetylchloride at −78° C. to obtain the desired product 15.

We recognized that 4-ferrocenylbenzyl alcohol could serve as a versatileintermediate in the synthesis of a variety of ferrocene derivatives.Arylation of ferrocene using commercially available 4-aminobenzylalcohol following a general synthetic outline (Nesmeyanov et al., (1954)Dokl. Akad. Nauk S.S.S.R., 97: 459-462; Broadhead et al., (1955) J.Chem. Soc, 367-370; Weinmayr (1955) Am. Chem. Soc., 77: 3012-3014)afforded 4-ferrocenylbenzyl alcohol (16) and 4-ferrocenylbenzaldehyde(17) which were separated chromatographically (Scheme 5, FIG. 52). It islikely that the oxidation of the alcohol to the aldehyde occurred bynitrous acid generated from reaction of NaNO₂ with HCl. This reactionprovides a new and simple way to prepare aldehyde 17. Subsequentborohydride reduction of aldehyde 17 gave alcohol 16 in 95% yield.Alternatively, treatment of ferrocene with the diazonium salt of ethyl4-aminobenzoate afforded ferrocenyl ester 18 (Nesmeyanov (1958) Proc. R.Soc. London, Ser. A, 246: 495-501; Akiyama et al. (1977) Bull. Chem.Soc. Jpn., 50: 1137-1141; Shimizu et al., (1983) Bull. Chem. Soc. Jpn.,56: 2023-2028). Reduction of 18 gave alcohol 16 (Scheme 5, FIG. 52).

Treatment of alcohol 16 with PPh₃ and CBr₄ in dry ether at roomtemperature for 12 h afforded 4-(bromomethyl)phenylferrocene (19) in 90%yield (Scheme 6, FIG. 53). Reaction of 19 with potassium thioacetate inDMF (Zhang et al. (1999) Tetrahedron Lett., 40: 603-606) at roomtemperature for 16 h afforded 4-[S-(acetylthio)methyl]phenylferrocene(20) in 81% yield.

We also prepared a set of S-acetylthio-derivatized alkylferrocenes withdifferent length alkyl chains for comparative studies. One member ofthis set (29) has been prepared previously (Chidsey et al. (1990) J. Am.Chem. Soc, 112: 4301-4306). Two closely related approaches to theS-acetylthio-derivatized alkylferrocenes have been established (Chidseyet al. (1990) J. Am. Chem. Soc., 112: 4301-4306; Creager et al. (1994)J. Electroanal. Chem., 370: 203-211), one of which is the route wefollowed to prepare a systematic set of compounds. The first stepinvolves Friedel-Crafts acylation of ferrocene with the appropriatebromoalkanoyl chloride (Scheme 7, FIG. 54). The established routeemployed 6-bromohexanoyl chloride, followed by reduction of the carbonylgroup to form the 6-(ferrocenyl)hexyl bromide (24) (Creager et al.(1994) J. Electroanal. Chem., 370, 203-211). Similar treatment offerrocene with 12-bromododecanoyl chloride or 16-bromohexadecanoylchloride gave the respective acylated ferrocenes (22, 23), which uponClemmensen reduction gave 12-ferrocenyldodecyl bromide (25) and16-ferrocenylhexadecyl bromide (26), respectively. Reaction of eachferrocenyl alkyl bromide (24-26) with potassium thioacetate afforded therespective S-acetylthio derivatized long-chain ferrocene (27-29) in goodyield.

Ferrocene-Porphyrin-Thiols

The synthesis of the thiol-derivatized ferrocene-porphyrins requiresaccess to ferrocenyl aldehydes. Among three desired ferrocenylaldehydes, ferrocenecarboxaldehyde is available commercially, and4-ferrocenylbenzaldehyde 17 was already obtained using several differentapproaches (Egger et al. (1964) Monatsch. Chem., 95: 1750-1758; Shih etal., (1965) K'o Hsueh T'ung Pao, 1: 78-79. CA 63:13314b; Moiseev et al.,(1988) Koord. Khim., 14: 328-331; Coe et al. (1993) J. Organomet. Chem,464: 225-232; Coles et al. (1997) J. Chem. Soc. Perkin Trans. 1:881-886). The serendipitous preparation of 17 from ferrocene and4-aminobenzyl alcohol (vide supra) represents one of the most efficientpreparations to date. Alternatively 4-ferrocenylbenzaldehyde 17 can beobtained from 4-ferrocenylbenzyl alcohol via oxidation using pyridiniumchlorochromate. The diphenylethyne-linked ferrocene carboxaldehyde 30was synthesized via Pd-coupling of ethynylphenylferrocene 4 with4-iodobenzaldehyde in 85% yield (eqn 1, FIG. 45).

Each of the target porphyrins bears three different meso substituents(AB₂C type). One route to AB₂C-porphyrins involves a mixed condensationof one dipyrromethane and two aldehydes, forming three porphyrinproducts. The latter are then separated chromatographically. Thisoverall synthetic route has been augmented recently by the developmentof non-scrambling conditions for the condensation, which ensures thatthe resulting mixture consists of no more than the expected threeporphyrins. Two sets of non-scrambling conditions have been identified(BF₃-etherate and NH₄Cl in CH₃CN at 0° C., or 17.8 mM TFA in CH₂Cl₂ atrt) (Littler et al. (1999) S. J. Org. Chem., 64: 2864-2872). While notelegant, this route is expedient if the three porphyrins can be readilyseparated. The difficulty of this separation depends on the differencein polarity imparted by the substituents on the two aldehydes. In thecourse of this study, we found that the N-ethylcarbamoyl or the acetylgroup attached to the thiophenol moiety (aldehyde 31 or 32) providesmoderate polarity, thereby facilitating separation of the porphyrinmixtures.

The condensation of 4-ferrocenylbenzaldehyde (17),4-[S—(N-ethylcarbamoyl)thio]-benzaldehyde 32 (Gryko et al. (1999) J.Org. Chem., 64: 8635-8647), and 5-mesityldipyrromethane (Lee et al.91994) Tetrahedron, 50: 11427-11440; Littler et al. (1999) J. Org.Chem., 64: 1391-1396) in the presence of BF₃-etherate and NH₄Cl inacetonitrile at 0° C. followed by oxidation with DDQ afforded the crudeporphyrin mixture (containing porphyrin 34) (Scheme 8. FIG. 55). Themixture was treated with zinc acetate and upon final purificationporphyrin Zn-34 was obtained in 3% yield (from aldehyde 31). Therelatively low yield of porphyrin Zn-34 prompted us to perform the samecondensation with TFA in CH₂Cl₂, which have proved for stericallyhindered dipyrromethanes (Littler (1999) supra.). Additionally wedecided to replace DDQ with p-chloranil (which is a weaker oxidant andthereby is less prone to oxidize the ferrocene moiety).Diisopropylethylamine (DIEA) also was added to neutralize the acid priorto oxidation (as acids are known to increase the oxidation potential ofquinones) (Fukuzumi et al. (1987) J. Chem. Soc., Perkin Trans. II,751-760). In this manner, porphyrin Zn-34 was obtained in 19% yield(from aldehyde 31).

The synthesis of porphyrin Zn-33 from ferrocenecarboxaldehyde,5-mesityldipyrro-methane and 4-(S-acetylthio)benzaldehyde (Gryko (1999)supra) was performed under both types of reaction conditions. Bothconditions afforded much higher yields of porphyrin Zn-33 (9.4% in MeCN,37% in CH₂Cl₂, from aldehyde 32) in comparison to porphyrin Zn-34. Thelatter result is astonishing because the best yield obtained to date forthe condensation of 5-mesityldipyrromethane and any aldehyde yielding anA₂B₂-porphyrin in a non-statistical process is 48% (Littler et al.(1999) supra.); yet in this case the AB₂C-porphyrin is formed in astatistical reaction. Careful analysis by TLC and LD-MS showedsignificant skewing from the statistical ratio of the three expectedporphyrins (which should be 1:2:1).

The synthesis of porphyrin 35 was performed only in the conditionsaffording higher yields (i.e., TFA in CH₂Cl₂/DIEA/p-chloranil). In thismanner, aldehyde 30 was converted to porphyrin 35 in a yield of 10.3%.Upon metalation, Zn-35 was obtained in 70% yield. Thus a significantdecrease in yield was discerned upon moving from ferrocenecarboxaldehyde(37%) through 17 (19%) to 30 (10%). It is noteworthy that TLC analysisas well as LD-MS analysis of the crude reaction mixtures showed no signof scrambling in these reactions.

In order to synthesize the porphyrin bearing two lateral ferrocenes(Zn-37) we needed the corresponding dipyrromethane 36. Treatment of4-ferrocenylbenzaldehyde 17 with excess pyrrole at room temperatureusing a standard procedure (Lee et al. (1994) Tetrahedron, 50:11427-11440; Littler et al. (1999) supra.) afforded 36 in 94% yield (eqn2, FIG. 46). The reaction of ferrocenyldipyrromethane 36,4-(S-acetylthio)benzaldehyde 31 and 4-methylbenzaldehyde provided thethree expected porphyrins (FIG. 47). After purification the desiredporphyrin 37 was isolated, contaminated with some undefined species.Conversion to the zinc chelate enabled purification of Zn-37 (0.33%yield) by column chromatography. The source of the surprisingly lowyield of porphyrin 37 has not been unequivocally established, but twopossibilities involve DDQ-mediated oxidation of the ferrocene moietiesor precipitation of the porphyrinogen. Thus the reaction was repeatedwith replacement of DDQ with p-chloranil and addition of a significantamount of THF to the reaction mixture upon initiation of the oxidationstep. The free base thus obtained was converted to the zinc chelate in3.1% yield (from dipyrromethane 36) (which represents an appreciableincrease in yield). The low yield of metalation is partially due to afree base impurity and partially due to a side reaction which createdundefined species that bound on the origin of TLC. In summary, theyields of some of the porphyrins were quite low, though sufficientmaterial was obtained for electrochemical characterization.

Electrochemical Studies

The electrochemical behavior of the ferrocenes and Znferrocene-porphyrins was investigated for samples both in solution andself-assembled on gold. The solution oxidation potentials of all theferrocenes are similar to one another (E_(1/2)˜0.2 V vs Ag/Ag⁺) andsimilar to that of unsubstituted ferrocene (E_(1/2)=0.19 V vs Ag/Ag⁺).The solution electrochemistry of the Zn ferrocene-porphyrins ischaracterized by three resolved oxidation waves (not shown). These wavescorrespond to the oxidation of the ferrocene constituent(s) and the twooxidations of the Zn porphyrin. In the case of Zn-37, the wave due toferrocene corresponds to the overlapping waves of the two identicalferrocene constituents. For Zn-34, Zn-35, and Zn-37, the oxidationpotentials for the ferrocene constituent(s) and the porphyrin areessentially identical to those of a the isolated components (Zn—P,E_(1/2)(1) ˜0.6 V; E_(1/2)(2) ˜0.9 V; ferrocene, E_(1/2)=˜0.20 V versusAg/Ag⁺). This result indicates that the ferrocene constituent(s) and theZn porphyrins are electrically isolated from one another. In the case ofZn-33, the potentials for all three oxidations are shifted negatively by˜0.1 V. This shift is attributed to conjugative interactions that occurbecause the ferrocene is directly bound to the porphyrin.

The ferrocenes and the Zn ferrocene-porphyrins bearing the differentlinkers all form self-assembled monolayers (SAMs) on gold via in situcleavage of the S-acetyl protecting group. The SAMs of all theferrocenes and Zn ferrocene-porphyrins are electrochemically robust andexhibit one (ferrocenes) or three (Zn ferrocene porphyrins) reversibleoxidation waves. In fast-scan (100 V/s) cyclic voltammograms of the SAMsof two ferrocenes (27 and 20) and two Zn ferrocene-porphyrins (Zn-34 andZn-37), respectively, the E_(1/2) values for the ferrocene SAMs areshifted slightly more positive (0.05 V or less) than those observed insolution. The E_(1/2) values for the ferrocenes and the Zn porphyrins inthe Zn ferrocene-porphyrin SAMs are each shifted by ˜0.15 V morepositive than those observed in solution. This trend parallels thatpreviously reported for SAMs of both ferrocenes (Creager et al. (1994)J. Electroanal. Chem., 370: 203-211) and porphyrins. The observationthat the voltammograms of the Zn-34 and Zn-37 SAMs are generally similarindicates that positioning the ferrocene substituents either on top of(Zn-34) or at the sides of (Zn-37) the porphyrin is a viable design forconstructing multiple bit information storage elements. However, theformer design offers the advantage of a smaller molecular area andtherefore, a higher packing density.

Conclusions

Ferrocene has been the benchmark for a wide variety of electrochemicalstudies of self-assembled monolayers on electroactive surfaces. Mostprior studies have employed ferrocene alkanethiols. The facile in situdeprotection of the S-acetyl protecting group on gold surfaces hasmotivated the synthesis of S-acetyl protected ferrocenylalkanethiolderivatives. A set of ferrocene-porphyrins bearing an attached thiolunit have been prepared for studies of the effects of molecularstructure on information storage properties (writing/reading rates,persistence of memory). Non-scrambling conditions foraldehyde-dipyrromethane condensations facilitated the synthesis of theAB₂C-type ferrocene-porphyrin-thiol structures. A small set offerrocene-aldehydes enabled the preparation of the correspondingferrocene-porphyrins. Each ferrocene-porphyrin is designed for verticalorganization on an electroactive surface yet possesses a distinctlocation of the ferrocene in the molecular architecture. Each of theferrocene-porphyrins forms a SAM that exhibits robust, reversibleelectrochemistry. Collectively, the studies indicated that all of thearchitectures examined are potential candidates for multi-bit molecularinformation storage elements.

Experimental Section

General

All chemicals obtained commercially were used as received unlessotherwise noted. Reagent grade solvents (CH₂Cl₂, CHCl₃, hexanes) andHPLC grade solvents (acetonitrile, toluene) were used as received fromFisher Scientific. Unless otherwise indicated, all solvents wereobtained from Fisher Scientific. Pyrrole was distilled from CaH₂. Allreported NMR spectra were collected in CDCl₃ (¹H NMR at 300 MHz; ¹³C NMRat 75 MHz). UV-Vis absorption and fluorescence spectra were recorded inCH₂Cl₂ or toluene as described previously (Li et al. (1997) J. Mater.Chem., 7: 1245-1262; Li et al. (1999) J. Am. Chem. Soc., 121:8927-8940). Flash chromatography was performed on flash silica (Baker,200-400 mesh) or alumina (Fisher, 80-200 mesh). Mass spectra wereobtained via laser desorption (LD-MS) in the absence of an added matrix(Fenyo et al. (1997) J. Porphyrins Phthalocyanines, 1: 93-99), fast atombombardment (FAB-MS, 10 ppm elemental compositional accuracy for theporphyrins), or electron-impact mass spectrometry (EI-MS). Porphyrinmetalation was monitored by fluorescence emission and excitationspectroscopy. After elution, the TLC plates were visualized with UVlight or sprayed with a solution of p-methoxybenzaldehyde (26 mL),glacial acetic acid (11 mL), concentrated sulfuric acid (35 mL), and 95%ethanol (960 mL) followed by heating (Gordon et al. (1972) The Chemist'sCompanion, Wiley-Interscience, New York:, p. 379]. All solvents weredried by standard methods prior to use. 4-iodobenzaldehyde was obtainedfrom Karl Industries, Ltd. Ethynylferrocene 9 (Doisneau et al. (1992) J.Organomet. Chem., 425: 113-117), 5-(ferrocenylcarbonyl)pentyl bromide 22and 6-ferrocenylhexyl bromide 25 were prepared according to the reportedprocedures (Creager et al. (1994) J. Electroanal. Chem. 370: 203-211).

4-Iodophenylferrocene (1)

4-Iodoaniline (8.8 g, 40 mmol) was suspended in a mixture of conc. HCl(20 mL) and H₂O (50 mL) and cooled to 0° C. A solution of NaNO₂ (3.3 g,48 mmol) in H₂O (10 mL) was added dropwise with stirring while thetemperature was carefully maintained at 0-5° C. After the addition wascompleted, the mixture was stirred for 30 min at 0° C. The resultingdiazonium salt solution was then added slowly to a solution of ferrocene(3.7 g, 20 mmol) in toluene (100 mL) at 0° C. An instantaneous evolutionof gas was observed. After complete addition, the reaction mixture wasstirred at 0° C. for 1 h. Then the mixture was warmed to rt and stirringwas continued for 16 h. The layers were separated and the aqueous layerwas extracted with toluene (3×100 mL). The combined organic layers werewashed with satd aq NaHCO₃ (3×100 mL), brine (3×100 mL), dried (MgSO₄)and filtered. The solvent was removed under reduced pressure and theresulting residue was purified by column chromatography (silica,petroleum ether/diethyl ether, 10:2) to afford 4.2 g (55%) of an orangesolid: mp 119-121° C.; ¹H NMR δ 4.02 (s, 5H), 4.33 (t, J=1.5 Hz, 2H),4.61 (t, J=1.5 Hz, 2H), 7.20, 7.58 (AA′BB′, J=7.8 Hz, 4H); ¹³C NMR δ66.4, 69.2, 69.7, 84.1, 90.5, 127.9, 137.3, 139.2; FAB-MS obsd 387.9420calcd exact mass 387.9411 (C₁₆H₁₃FeI).

4-(S-Acetylthio)phenylferrocene (2)

Following a general procedure for lithiation and sulfur trapping (Joneset al., (1970) Org. Syn., 50: 104) followed by acetylation (Pearson etal. (1997) J. Org. Chem., 62: 1376-1387), a solution of 1 (2.0 g, 5.1mmol) in dry THF (20 mL) under argon at −78° C. was stirred and treatedwith tert-butyllithium (3.1 mL, 5.2 mmol, 1.7 M in pentane) dropwiseover a period of 10 min. The mixture was stirred at −78° C. for anadditional 5 min. Elemental sulfur (0.16 g, 5.2 mmol) in dry THF (40 mL,0° C.) was added in one portion, and the mixture was allowed to warm to0° C. for 30 min. The mixture was cooled to −78° C., and acetyl chloride(0.60 g, 5.2 mmol) was added in one portion. The reaction mixture waswarmed to rt overnight, poured into rapidly stirred ice-water (50 mL),extracted with CH₂Cl₂ (3×50 mL) and dried (MgSO₄). The solvent wasremoved and the residue was purified by flash column chromatography(silica, petroleum ether/diethyl ether, 10:1) to afford 1.5 g (85%) ofan orange solid: mp 108-110° C.; ¹H NMR δ 2.42 (s, 3H), 4.12 (s, 5H),4.22 (t, J=1.5 Hz, 2H), 4.42 (t, J=1.5 Hz, 2H), 7.35, 7.50 (AA′BB′,J=8.5 Hz, 2×2H); ¹³C NMR δ 30.2, 66.7, 69.3, 69.7, 84.1, 124.7, 126.8,134.3, 141.2, 194.4; FAB-MS obsd 336.0297, calcd exact mass 336.0271;Anal. Calcd for C₁₈H₁₆FeOS: C, 64.30; H, 4.80. Found: C, 64.29; H, 4.83.

4-[2-(Trimethylsilyl)ethynyl]phenylferrocene (3)

Method 1.

Samples of 1 (2.0 g, 5.2 mmol), CuI (5.0 mg, 26 μmol) and PdCl₂(PPh₃)₂(30 mg, 43 μmol) were dissolved in freshly distilled TEA (40 mL). Theflask was then evacuated and purged with argon (3 times) on a Schlenkline. (Trimethylsilyl)acetylene (0.78 mL, 5.5 mmol) was added dropwiseunder stirring. After the addition was complete, the reaction mixturewas heated to 50° C. and sealed for 4 h at this temperature. The solventwas removed under reduced pressure to give a red oil. Purification bycolumn chromatography (silica, petroleum ether/ethyl ether, 10:3)afforded 1.6 g (85%) of a red-orange solid: mp 110-112° C.

Method 2.

4-[2-(Trimethylsilyl)ethynyl]aniline (Takahashi et al. (1980) Synthesis,8: 627-630) (1.0 g, 5.3 mmol) was suspended in a mixture of conc. HCl(2.4 mL) and H₂O (10 mL) and cooled to 0° C. under stirring. A solutionof NaNO₂ (0.40 g, 5.8 mmol) in H₂O (2 mL) was added while thetemperature was carefully maintained between 0-5° C. After the additionwas complete, the mixture was stirred for 30 min at 0° C. The resultingdiazonium salt solution was then added slowly to a solution of ferrocene(0.49 g, 2.7 mmol) in toluene (100 mL) at 0° C., resulting in gasevolution. After the addition was complete, the mixture was stirred for1 h at 0° C., warmed to rt and stirring was continued for an additional16 h. The layers were separated and the aqueous layer was extracted withtoluene (3×50 mL). The combined organic layers were washed with satd aqNaHCO₃ (3×50 mL), brine (3×50 mL), dried (MgSO₄) and filtered. Thesolvent was removed under reduced pressure and the resulting residue waspurified by column chromatography (silica, CH₂Cl₂/hexanes, 1:1) toremove unreacted ferrocene. Elution with CH₂Cl₂ afforded 0.42 g (44%) ofcompound 3. ¹H NMR δ 0.27 (s, 9H), 4.02 (s, 5H), 4.35 (A₂B₂, J=1.5 Hz,2H), 4.65 (A₂B₂, J=1.5 Hz, 2H), 7.40 (s, 4H); ¹³C NMR δ 0.04, 66.5,69.3, 69.7, 84.1, 94.0, 105.5, 120.2, 125.6, 132.0, 140.1; FAB-MS obsd358.0851, calcd exact mass 358.0840 (C₂₁H₂₂FeSi).

4-(Ethynyl)phenylferrocene (4)

A solution of 3 (1.5 g, 4.2 mmol) in anhydrous THF/MeOH (2:1, 30 mL) wastreated with K₂CO₃ (1.2 g, 8.4 mmol) and the mixture was stirred at rtfor 30 min. The solvent was removed under reduced pressure affording anorange solid. The residue was dissolved in ether (50 mL), washed withH₂O (3×50 mL), dried (MgSO₄) and filtered. The solvent was removed underreduced pressure. Purification by column chromatography (silica,petroleum ether/ethyl ether, 10:2) afforded an orange solid (1.0 g,90%): mp 104-106° C.; ¹H NMR δ 3.11 (s, 1H), 4.04 (s, 5H), 4.35 (t,J=2.4 Hz, 2H), 4.65 (t, J=2.4 Hz, 2H), 7.42 (s, 4H); ¹³C NMR δ 66.5,69.3, 69.7, 84.0, 94.1, 105.5, 120.3, 125.7, 132.1, 140.3; FAB-MS obsd286.0460, calcd exact mass 286.0445 (C₁₈H₁₄Fe). Physical propertiesconcur with published data (Simionescu et al. (1976) J. Organomet.Chem., 113: 23-28).

4-{2-[4-(S-Acetylthio)phenyl]ethynyl}phenylferrocene (5)

Method 1:

Samples of 4 (1.0 g, 3.5 mmol), CuI (2.5 mg, 13 μmol), (PPh₃)₂PdCl₂ (6.0mg, 13 μmol) and 1-iodo-4-(S-acetylthio)benzene [Gryko, D. T., et al.,submitted, companion paper 1] (1.0 g, 3.9 mmol) were added to a 50 mLSchlenk flask. The flask was evacuated and purged with argon (3 times)on the Schlenk line. Then freshly distilled and degassed DIEA (1.3 mL,7.0 mmol) and THF (5 mL) were added. The flask was placed in a preheatedoil bath (40° C.) and sealed. The mixture was stirred for 4 h at 40° C.,cooled to rt and filtered. The filter cake was washed with CH₂Cl₂ (3×10mL). The filtrate was washed with water (3×20 mL) and satd aq NaCl anddried (MgSO₄). The solvents were removed and the residue was purified byflash column chromatography (silica, petroleum ether/diethyl ether,10:2) to afford a red solid (1.3 g, 88%).

Method 2:

4-Iodophenylferrocene (1, 1.0 g, 2.5 mmol), CuI (2.5 mg, 13 μmol),(PPh₃)₂PdCl₂ (6.0 mg, 13 μmol), 8 (0.5 g, 3.0 mmol) and DIEA (1.3 mL,7.0 mmol) were added to a 50 mL Schlenk flask. The flask was thenevacuated and purged with argon (3 times) on a Schlenk line. Thenfreshly distilled and degassed THF (5 mL) was added. The flask wassealed and the mixture was stirred for 24 h at rt and filtered. Thefilter cake was washed with CH₂Cl₂ (3×10 mL). The filtrate was washedwith water (3×20 mL) and satd aq NaCl and dried (MgSO₄). The solvent wasremoved and the residue was purified by flash column chromatography(silica, petroleum ether/diethyl ether, 10:2) to afford a red solid (1.0g, 90%). mp 118-120° C.; IR(KBr) ν/cm⁻¹: 2253.6 (s), 1794.0 (w), 1474.4(m), 1382.1 (w), 1105.6 (m), 1003 (m); ¹H NMR δ 2.44 (s, 3H), 4.04 (s,5H), 4.36 (A₂B₂, J=1.5 Hz, 2H), 4.67 (A₂B₂, J=1.5 Hz, 2H), 7.39, 7.554.67 (AA′BB′, J=8.7 Hz, 2×2H), 7.45 (s, 4H); ¹³C NMR δ 31.0, 67.2, 67.3,70.1, 70.4, 70.6, 71.0, 89.4, 92.2, 125.5, 126.5, 132.4, 132.8, 133.2,133.3, 134.9, 140.9, 193.2; FAB-MS obsd 436.0595, calcd exact mass436.0584; Anal. Calcd for C₂₆H₂₀FeOS: C, 71.57; H, 4.62. Found: C,71.56; H, 4.64.

1-Iodo-4-[2-(trimethylsilyl)ethynyl]benzene (6)

To a mixture of (trimethylsilyl)-acetylene (2.0 mL, 14 mmol) and1,4-diiodobenzene (9.4 g, 28 mmol) in freshly distilled TEA (40 mL) andTHF (20 mL) in a 100 mL Schlenk flask were added CuI (0.19 g, 1.0 mmol)and PdCl₂(PPh₃)₂ (0.30 g, 0.43 mmol) with stirring. The flask was thenevacuated and purged with argon (3 times) on a Schlenk line. The mixturewas heated at 40° C. (oil bath), sealed and stirred for 4 h. Thesolvents were removed under reduced pressure. The residue was dissolvedin ethyl ether (150 mL), washed with H₂O (3×100 mL), dried (MgSO₄) andfiltered. The solvent removed under reduced pressure. The resultingresidue was purified by column chromatography (silica, petroleumether/ethyl ether, 10:1) to afford 5.5 g (85%) of an off-white solid. mp57-59° C. (lit.²⁵ 56-58° C.); ¹H NMR δ 0.33 (s, 9H), 7.18, 7.64 (AA′BB′,J=8.7 Hz, 2×2H); ¹³C NMR δ 0.24, 94.2, 96.1, 102.6, 123.4, 133.5, 137.8;FAB-MS obsd 299.9821, calcd exact mass 299.9882 (C₁₁H₁₃ISi).

1-(S-Acetylthio)-4-[2-(trimethylsilyl)ethynyl]benzene (7)

Following a general procedure for lithiation and sulfur trapping [Joneset al., (1970) Org. Syn., 50: 104) followed by acetylation (Pearson etal (1997) J. Org. Chem., 62: 1376-1387), a solution of 6 (2.0 g, 6.3mmol) in dry THF (20 mL) was stirred under argon at −78° C. and treatedwith tert-butyllithium (3.8 mL, 6.3 mmol, 1.7 M in pentane) dropwiseover a 10 min period. The mixture was stirred at −78° C. for additional5 min. A cold slurry of elemental sulfur (0.2 g, 6.3 mmol) in dry THF(40 mL, 0° C.) was added in one portion, and the mixture was warmed to0° C. in 30 min. The flask was cooled to −78° C., and acetyl chloride(0.8 g, 6.5 mmol) was added in one portion. The yellow mixture waswarmed to rt overnight, then poured into rapidly stirred ice-water (50ml), extracted with CH₂Cl₂ (3×50 mL) and dried (MgSO₄). The solventswere removed and the residue was purified by flash column chromatography(silica, petroleum ether/diethyl ether, 10:1) to afford a yellow solid(1.4 g, 80%): mp 45-47° C. (lit.⁴² 42-44° C. ); ¹H NMR δ 0.25 (s, 9H),2.41 (s, 3H), 7.34, 7.48 (AA′BB′, J=8.7 Hz, 2×2H); ¹³C NMR δ 31.3, 97.0,105.5, 125.3, 129.4, 133.9, 135.5, 195.2; FAB-MS obsd 248.0713, calcdexact mass 248.0718 (C₁₃H₁₆OSSi).

2-(4-Iodophenyl)ethynylferrocene (10)

Following the procedure for preparing 6, samples of 9 (Doisneau et al.(1992) J. Organomet. Chem. 425: 113-117) (1.0 g, 9.6 mmol),1,4-diiodobenzene (3.0 g, 20 mmol), PdCl₂(PPh₃)₂ (30 mg, 43 μmol) andCuI (5.0 mg, 26 μmol) were reacted in THF (20 mL) and Et₃N (20 mL). Thereaction mixture was stirred at 50° C. for 5 h and worked up. Theresulting residue was purified by column chromatography (silica,petroleum ether) to afford 1.9 g (95%) of a red-brown solid. ¹H NMR δ4.24 (s, 5H), 4.25 (s, 2H), 4.50 (s, 2H), 7.21, 7.65 (AA′BB′, J=8.7 Hz,2×2H); ¹³C NMR δ 66.3, 68.8, 70.5, 72.0, 85.1, 91.1, 124.6, 127.4,133.5, 137.8; FAB-MS obsd 411.9439, calcd exact mass 411.9436(C₁₈H₁₃FeI). Spectral and physical properties concur with published data(Yu et al. (1999) J. Org. Chem. 64: 2070-2079).

2-[4-(S-Acetylthio)phenyl]ethynylferrocene (11)

Following a general procedure for lithiation and sulfur trapping [Jones,E., et al., Org. Syn. 1970, 50, 104] followed by acetylation (Pearson etal. (1997) J. Org. Chem., 62: 1376-1387), samples of 10 (1.0 g, 2.4mmol), t-BuLi (3.0 mL, 5.1 mmol, 1.7 M in pentane), elemental sulfur(0.092 g, 2.9 mmol) and acetyl chloride (0.8 mL, 2.9 mmol) were reactedin dry THF under −78° C. The reaction mixture was allowed to warm to rtfor 16 h and worked up. The resulting residue was purified by columnchromatography (silica, petroleum ether:ether, 10:1) to afford 0.81 g(95%) of a red-brown solid. mp 113-115° C. (lit.²⁵ 96-98° C.); ¹H NMR δ2.44 (s, 3H), 4.25 (s, 5H), 4.26 (t, J=1.5 Hz, 2H), 4.51 (t, J=1.5 Hz,2H), 7.18, 7.64 (AA′BB′, J=8.1 Hz, 2×2H); ¹³C NMR δ 30.1, 65.1, 69.2,70.5, 71.7, 85.0, 90.6, 125.3, 127.3, 133.0, 134.4, 198.0; FAB-MS obsd360.0270, calcd exact mass 360.0269 (C₂₀H₁₆FeOS).

1-Acetyl-1′-ethylferrocene (12)

1,1′-Diacetylferrocene (5.0 g, 20 mmol) in toluene (20 mL) was added toa freshly prepared mixture of zinc/mercury amalgam (3.0 g of granulatedZn, 0.2 g of HgCl₂), 10 M HCl (20 mL) and water (20 mL). The reactionmixture was heated to reflux for 4 h with vigorous stirring. The mixturewas cooled to rt and extracted with toluene (3×50 mL) and the organiclayer was washed with water (3×100 mL) and satd aq NaHCO₃ (3×50 mL). Theorganic layer was dried (MgSO₄), evaporated, and chromatographed(silica, petroleum ether:ether, 1:10) to afford 2.8 g (60%) of ared-brown oil. ¹H NMR δ 1.13 (t, J=7.5 Hz, 3H), 2.26 (q, J=7.5 Hz, 2H),2.36 (s, 3H), 4.08 (s, 4H), 4.44 (t, J=2.1 Hz, 2H), 4.69 (t, J=2.1 Hz,2H); ¹³C NMR δ 15.4, 22.2, 28.2, 69.8, 69.9, 70.7, 73.6, 92.5, 202.8;FAB-MS obsd 256.0544, calcd exact mass 256.0551 (C₁₄H₁₆FeO). Spectraland physical properties concur with published data (Rosenblum et al.(1958) J. Am. Chem. Soc., 80: 5443-5448).

1-Ethyl-1′-ethynylferrocene (13)

Following a general procedure (Doisneau et al. (1992) J. Organomet.Chem. 425: 113-117), to a solution of 12 (2.0 g, 7.8 mmol) in dry THF(50 mL) at −78° C. were added dropwise 1.1 equiv of freshly prepared LDA(40 mL, 8.0 mmol) in THF. After 1 h at −78° C., diethyl chlorophosphate(1.1 equiv, 1.2 mL, 8.0 mmol) was added at −78° C. for 1 h. The reactionmixture was allowed to warm to rt for an additional 1 h and then wasrecooled to −78° C. and an additional 2.3 equiv of LDA (80 mL, 20 mmol)was added. The reaction mixture was warmed to rt and stirred overnightthen hydrolyzed at 0° C. The reaction mixture was extracted with ether(3×50 mL) and the combined organic layers were washed with water (3×50mL) and satd NaCl (3×50 mL) and dried (MgSO₄). The resulting residueafter evaporation was purified by column chromatography (silica,petroleum ether) to afford 1.7 g (90%) of a yellow oil. ¹H NMR δ 1.19(t, J=7.5 Hz, 3H), 2.36 (q, J=7.5 Hz, 2H), 2.73 (s, 1H), 4.10 (m, 4H),4.15 (t, J=2.1 Hz, 2H), 4.37 (t, J=2.1 Hz, 2H); ¹³C NMR δ 15.3, 21.9,66.5, 69.7, 69.8, 70.0, 72.9, 74.3; FAB-MS obsd 238.0466, calcd exactmass 238.0445; Anal. Calcd for C₁₄H₁₄Fe: C, 70.62; H, 5.93. Found: C,70.65; H, 5.92.

1-Ethyl-1′-[2-(4-iodophenyl)ethynyl]ferrocene (14)

Following the procedure for preparing 6, samples of 13 (1.0 g, 4.2mmol), 1,4-diiodobenzene (2.8 g, 8.5 mmol), PdCl₂(PPh₃)₂ (30 mg, 43μmol) and CuI (5.0 mg, 26 μmol) were reacted in THF (20 mL) and Et₃N (20mL). The reaction mixture was stirred at 50° C. for 5 h and worked up.The resulting residue was purified by column chromatography (silica,petroleum ether) to afford 1.8 g (95%) of a red-brown solid. mp 55-57°C.; ¹H NMR δ 1.17 (t, J=7.5 Hz, 3H), 2.35 (q, J=7.5 Hz, 2H), 4.10 (s,4H), 4.18 (t, J=2.1 Hz, 2H), 4.40 (t, J=2.1 Hz, 2H), 7.18, 7.64 (AA′BB′,J=8.1 Hz, 2×2H); ¹³C NMR δ 15.5, 22.3, 67.0, 68.9, 69.5, 70.2, 74. 5,91.2, 123.3, 133.5, 134.0, 135.8; FAB-MS obsd 439.8721, calcd exact mass439.8724 (C₂₀H₁₇FeI).

1-{2-[4-(S-Acetylthio)phenyl]-2-ethynyl}-1′-ethylferrocene (15)

Following a general procedure for lithiation and sulfur trapping (Joneset al. (1970) Org. Syn. 50: 104] followed by acetylation (Pearson et al.(1997) J. Org. Chem. 62: 1376-1387), samples of 14 (1.0 g, 2.3 mmol),t-BuLi (2.7 mL, 4.6 mmol, 1.7 M in pentane), elemental sulfur (0.09 g,2.8 mmol) and acetyl chloride (0.8 mL, 2.8 mmol) were reacted in dry THFunder −78° C. The reaction mixture was allowed to warm to rt for 16 hand worked up. The resulting residue was purified by columnchromatography (silica, petroleum ether:ether, 10:1) to afford 0.83 g(95%) of a red-brown solid. mp 83-85° C.; ¹H NMR δ 1.20 (t, J=7.2 Hz,3H), 2.40 (q, J=7.2 Hz, 2H), 2.42 (s, 3H), 4.12 (s, 4H), 4.22 (t, J=2.1Hz, 2H), 4.42 (t, J=2.1 Hz, 2H), 7.35, 7.50 (AA′BB′, J=8.1 Hz, 2×2H);¹³C NMR δ 15.1, 21.8, 30.9, 65.5, 69.6, 70.0, 70.1, 72.6, 132.5, 134.9,194.4; FAB-MS obsd 388.0644, calcd exact mass 388.0645; Anal. Calcd forC₂₂H₂₀FeOS: C, 68.05; H, 5.19. Found: C, 68.08; H, 5.24.

4-Ferrocenylbenzyl alcohol (16)

Method A:

A solution of 4-(carbethoxy)phenyl-ferrocene 18 (1.13 g, 3.40 mmol) inTHF (10 mL) was added via syringe to a suspension of LiAlH₄ (105 mg,2.70 mmol) in THF (10 mL). The mixture was heated to reflux under Ar for1 h. After 1 h TLC (silica, CH₂Cl₂) showed a new component (R_(f)=0.2)and no starting material (R_(f)=0.6). The reaction mixture was cooled to0° C. and then quenched by sequential addition of 200 μL H₂O, 200 μL 10%NaOH, and 600 μL H₂O (caution: exothermic reaction). The resultingslurry was poured into a mixture Et₂O (40 mL) and satd aq Rochelle'ssalt (60 ml) and stirred at rt until the aluminum salts dissolved (about20 min). The layers were separated, and the ethereal layer was washedwith H₂O (30 mL), brine (30 mL), and dried over MgSO₄. The solution wasevaporated to yield 878 mg of a yellow solid (87.8%).

Method B:

4-Aminobenzyl alcohol (3.0 g, 24 mmol) was suspended in a mixture ofconc. HCl (20 mL) and H₂O (20 mL) and cooled to 0° C. under stirring. Asolution of NaNO₂ (2.1 g, 30 mmol) in H₂O (10 mL) was added dropwisewhile the temperature was carefully maintained between 0-5° C. Theresulting mixture was stirred for 30 min at 0° C., then slowly added at0° C. to a solution of ferrocene (3.7 g, 20 mmol) in toluene (100 mL),resulting in gas evolution. After complete addition, the reactionmixture was stirred at 0° C. for 6 h and warmed to rt. Stirring wascontinued for another 6 h. The layers were separated and the aqueouslayer was extracted with toluene (3×100 mL). The combined organic layerswere washed with satd aq NaHCO₃ (3×100 mL), brine (3×100 mL), dried(MgSO₄) and filtered. The solvent was removed under reduced pressure andthe resulting residue was purified by column chromatography (silica,petroleum ether/diethyl ether, 10:2) to afford 0.94 g (20%) of4-ferrocenylbenzyl alcohol 16 (as well as 2.1 g (45%) of4-ferrocenylbenzaldehyde 17).

Method C:

Sodium borohydride (0.5 g, 14 mmol) was added to a cold (0° C.) solutionof 17 (2.0 g, 6.9 mmol) in methanol (20 mL) with stirring. Afterstirring for 40 min at 0° C., the mixture was neutralized with diluteHCl (10%) and extracted with diethyl ether (3×50 ml). The ether solutionwas dried (MgSO₄) and removed in vacuo to yield a yellow solid (1.9 g,95%). mp 109-111° C.; ¹H NMR δ 1.66 (t, J=6.0 Hz, 1H), 4.04 (s, 5H),4.31 (A₂B₂, J=1.5 Hz, 2H), 4.64 (A₂B₂, J=1.5 Hz, 2H), 4.66 (d, J=6 Hz,2H), 7.29, 7.47 (AA′BB′, J=8.7 Hz, 2×2H); ¹³C NMR δ 65.9, 67.2, 69.3,70.3, 85.7, 105.0, 127.0, 127.9, 139.0, 139.5; FAB-MS obsd 292.0631,calcd exact mass 292.0648; Anal. Calcd for C₁₇H₁₆FeO: C, 69.89; H, 5.52.Found: C, 70.03; H, 5.46.

4-Ferrocenylbenzaldehyde (17)

A sample of 4-ferrocenylbenzyl alcohol 16 (630 mg, 2.15 mmol) was addedto a suspension of pyridinium chlorochromate (1.22 g, 3.23 mmol) inCH₂Cl₂ (5 mL) and the mixture was stirred under argon at rt for 18 h.Then Et₂O (20 mL) was added and the mixture was filtered through a padof Celite. The filtrate was concentrated and chromatographed (silica,CH₂Cl₂/hexanes, 4:1) affording 306 mg (47.8%). TLC (silica, CH₂Cl₂),R_(f)=0.35; mp 122-125° C. (lit.^(35a) 121-125° C.); ¹H NMR δ 4.07 (s,5H), 4.46 (A₂B₂, J=1.5 Hz, 2H), 4.47 (A₂B₂, J=1.5 Hz, 2H), 7.60, 7.78(AA′BB′, J=8.7 Hz, 4H), 9.97 (s, 1H); ¹³C NMR δ 67.8, 70.5, 70.6, 70.8,127.0, 127.7, 130.7, 130.7, 134.7, 192.5; EI-MS obsd 290.0406 (M⁺),calcd exact mass 290.0394; Anal. Calcd for C₁₇H₁₄FeO: C, 70.37; H, 4.86.Found: C, 70.50; H, 4.81.

4-(Bromomethyl)phenylferrocene (19)

Triphenylphosphine (2.6 g, 10 mmol) and CBr₄ (3.3 g, 10 mmol) were addedto a solution of 16 (1.9 g, 6.6 mmol) in dry ether (50 mL) and themixture was stirred overnight under argon at rt. The precipitate wasfiltered off and the filtrate was evaporated in vacuo. The residue waspurified by column chromatography (silica, petroleum ether/diethylether, 10:1) to afford a red oil (1.9 g, 82%): ¹H NMR δ 4.06 (s, 5H),4.35 (s, 2H), 4.52 (s, 2H), 4.65 (s, 2H), 7.32, 745 (AA′BB′, J=8.5 Hz,2×2H); ¹³C NMR δ 33.1, 33.8, 67.1, 69.2, 70.0, 85.9, 127.4, 129.1,135.5, 138.9; FAB-MS obsd 355.0543, calcd exact mass 355.0548; Anal.Calcd for C₁₇H₁₅BrFe: C, 57.51; H, 4.26. Found: C, 57.59; H, 4.20.

4-[(S-Acetylthio)methyl]phenylferrocene (20)

Following a general procedure (Zhang et al. (1999) Tetrahedron Lett.,40: 603-606), a solution of 19 (1.5 g, 4.2 mmol) in DMF (10 mL) wasadded to a solution of potassium thioacetate (0.60 g, 5.0 mmol) in DMF(10 mL) and the mixture was stirred overnight at rt. The mixture wasfiltered and water was added to the filtrate. The filtrate was extractedwith ethyl ether (3×50 mL), and the combined organic layers were dried(MgSO₄) and evaporated in vacuo. The residue was purified by columnchromatography (silica, petroleum ether/diethyl ether, 10:1) affording ayellow solid (1.3 g, 90%): mp 79-81° C.; ¹H NMR δ 2.38 (s, 3H), 4.05 (s,5H), 4.12 (s, 2H), 4.31 (A₂B₂, J=1.5 Hz, 2H), 4.62 (A₂B₂, J=1.5 Hz, 2H),7.21, 7.41 (AA′BB′, J=8.5 Hz, 2×2H); ¹³C NMR δ 31.1, 34.0, 67.2, 69.6,70.3, 85.7, 127.0, 129.5, 135.7, 139.1, 196.1; FAB-MS obsd 350.0431,calcd exact mass 350.0428; Anal. Calcd for C₁₉H₁₈FeOS: C, 65.15; H,5.18. Found: C, 64.91; H, 5.15.

11-(Ferrocenylcarbonyl)undecyl bromide (22)

Following a general procedure for preparing 21 (Creager et al. (1994) J.Electroanal. Chem., 370: 203-211), a solution of 12-bromododecanoic acid(4.2 g, 15 mmol) in SOCl₂ (50 mL) was heated at 50° C. under argon for 1h. The excess SOCl₂ was removed by water pump distillation with benzene(3×50 mL). 4.3 g (95%) of 12-bromododecanoyl chloride was obtained as acolorless oil and used in the subsequent reaction without furtherpurification. In a 50 mL flask anhydrous AlCl₃ (2.8 g, 21 mmol) wasadded to a stirred solution of 12-bromododecanoyl chloride (4.0 g, 13.6mmol) in dry CH₂Cl₂ (30 mL) at 0° C. under argon for 20 min. Then themixture was added dropwise over 10 min to a solution of ferrocene (2.6g, 14 mmol) in CH₂Cl₂ (50 mL) at 0° C. The mixture was stirred andallowed to warm to rt. After 2 h water (30 mL) was added slowly intothis mixture. Then the phases were separated, and the organic layer waswashed with water (3×100 mL) and NaHCO₃ (2×50 mL) and over (MgSO₄). Thesolvent was evaporated in vacuo and the residue was purified by columnchromatography (silica, petroleum ether/diethyl ether, 10:3) to afford ared oil (4.3 g, 85%). ¹H NMR δ 1.28 (s, 16H), 1.64 (m, 2H), 2.63 (m,2H), 3.29 (m, 2H), 4.19 (s, 5H), 4.48 (A₂B₂, J=1.5 Hz, 2H), 4.78 (A₂B₂,J=1.5 Hz, 2H); ¹³C NMR δ 25.0, 28.5, 29.0, 30.1, 30.9, 33.3, 34.5, 40.5,70.0, 70.4, 72.9, 89.0, 205.0; FAB-MS obsd 446.0955, calcd exact mass446.0958 (C₁₂H₃₁.BrFeO).

15-(Ferrocenylcarbonyl)pentadecyl bromide (23)

16-Bromohexadecanoic acid (4.5 g, 14 mmol) in SOCl₂ (50 mL) was heatedat 50° C. under argon for 1 h. The excess SOCl₂ was removed by waterpump distillation with benzene (3×50 mL). 4.3 g (95%) of16-bomohexadecanoyl chloride was obtained as a colorless oil and used inthe subsequent reaction without further purification.16-Bromohexadecanoyl chloride (4.5 g, 13 mmol) was treated withferrocene (2.5 g, 14 mmol) following the same procedure as described for22 to form a brown oil (5.7 g, 85%): ¹H NMR δ 1.25 (s, 22H), 1.68 (m,2H), 1.84 (m, 2H), 2.68 (m, 2H), 3.39 (m, 2H), 4.18 (s, 5H), 4.47 (A₂B₂,J=1.5 Hz, 2H), 4.76 (A₂B₂, J=1.5 Hz, 2H); ¹³C NMR δ 25.3, 28.8, 29.4,30.1, 30.2, 30.3, 34.8, 40.4, 70.0, 70.4, 72.7, 89.1, 205.4; FAB-MS obsd502.1533, calcd exact mass 502.1535 (C₂₆H₃₉BrFeO).

12-Ferrocenyldodecyl bromide (25)

Following a general procedure for preparing 24 (Creager et al. (1994) J.Electroanal. Chem., 370: 203-211), to a freshly prepared zinc/mercuryamalgam (6.7 g granulated Zn, 0.4 g HgCl₂) in a 100 mL flask was added10 M HCl (40 mL) with stirring. A solution of 22 (3.0 g, 6.7 mmol) intoluene (40 mL) was added in one portion. The resulting two-phasemixture was heated to reflux and stirred vigorously. After 16 h underreflux, during which two 5 mL portions of 10 M HCl were added, thereaction flask was cooled to rt. The phases were separated, and theorganic layer was washed with water (3×100 mL) and dried (MgSO₄). Thesolvent was evaporated in vacuo and the residue was purified by columnchromatography (silica, petroleum ether/diethyl ether, 10:1) to afford abrown oil (2.6 g, 90%) that solidified upon standing in the freezer: mp40-42° C.; ¹H NMR δ 1.29 (s, 16H), 1.47 (m, 2H), 1.86 (m, 2H), 2.32 (m,2H), 3.42 (m, 2H), 4.05 (s, 2H), 4.06 (s, 2H), 4.10 (s, 5H); ¹³C NMR δ28.2, 28.8, 29.5, 29.6, 31.1, 32.9, 34.0, 67.0, 68.1, 68.5, 89.6; FAB-MSobsd 432.1114, calcd exact mass 432.1115 (C₂₂H₃₃BrFe).

16-Ferrocenylhexadecyl bromide (26)

15-(Ferrocenylcarbonyl)pentadecyl bromide 23 (1.5 g, 2.8 mmol) wastreated with zinc/mercury amalgam (2.8 g of granulated Zn, 0.3 g ofHgCl₂) as described for 25 to afford a yellow solid (1.3 g, 90%): mp52-54° C.; ¹H NMR δ 1.27 (s, 18H), 1.55 (m, 2H), 2.32 (m, 2H), 2.33 (s,3H), 2.87 (m, 2H), 4.05 (s, 2H), 4.07 (s, 2H), 4.11 (s, 5H); ¹³C NMR δ28.2, 28.8, 29.5, 29.6, 29.7, 31.1, 32.9, 34.0, 67.0, 68.1, 68.5, 88.9;FAB-MS obsd 488.1752, calcd exact mass 488.1741 (C₂₆H₄₁BrFe).

6-(S-Acetylthio)hexylferrocene (27)

Following a general procedure (Zhang et al. (1999), Tetrahedron Lett.40: 603-606), 6-ferrocenylhexyl bromide (24, 1.2 g, 3.5 mmol) in DMF (10mL) was added to a stirred solution of potassium thioacetate (0.51 g,4.5 mmol) in DMF (10 mL). The mixture was stirred at rt until TLC showedcomplete consumption of the ferrocene starting material (20 h). Themixture was filtered and water was added to the filtrate. The filtratewas extracted with ethyl ether (3×50 mL), and the combined organiclayers were dried (MgSO₄) and evaporated in vacuo. The residue waspurified by column chromatography (silica, petroleum ether/diethylether, 10:1) to afford a yellow oil (1.1 g, 90%) that solidified uponstanding in the freezer. mp 40-42° C.; ¹H NMR δ 1.35 (m, 4H), 1.50 (m,2H), 1.56 (m, 2H), 2.32 (t, J=7.2 Hz, 2H), 2.33 (s, 3H), 2.88 (t, J=7.2Hz, 2H), 4.05 (s, 4H), 4.10 (s, 5H); ¹³C NMR δ 29.4, 29.8, 30.2, 31.3,31.6, 67.7, 68.8, 69.2, 90.0, 196.0; FAB-MS obsd 344.0908, calcd exactmass 344.0897; Anal. Calcd for C₁₈H₂₄FeOS: C, 62.79; H, 7.03. Found: C,62.81; H, 7.03.

12-(S-Acetylthio)dodecylferrocene (28)

12-Ferrocenyldodecyl bromide 25 (2.0 g, 4.6 mmol) was treated withpotassium thioacetate (0.70 g, 6.0 mmol) for 20 h as described for 27 toform yellow crystals (1.8 g, 93%): mp 45-47° C.; ¹H NMR δ 1.27 (s, 18H),1.55 (m, 2H), 2.32 (m, 2H), 2.33 (s, 3H), 2.87 (m, 2H), 4.05 (s, 2H),4.07 (s, 2H), 4.11 (s, 5H); ¹³C NMR δ 29.5, 29.8, 30.2, 30.3, 30.3,31.3, 31.8, 67.7, 68.8, 69.2, 90.4, 196.8; FAB-MS obsd 428.1851, calcdexact mass 428.1836; Anal. Calcd for C₂₄H₃₆FeOS: C, 67.28; H, 8.47.Found: C, 67.25; H, 8.51.

16-(S-Acetylthio)hexadecylferrocene (29)

16-Ferrocenylhexadecyl bromide 26 (1.1 g, 2.3 mmol) was treated withpotassium thioacetate (0.4 g, 3.5 mmol) for 20 h following the sameprocedure described for 27 to afford yellow crystals (1.0 g, 93%): mp55-57° C.; ¹H NMR δ 1.25 (s, 22H), 1.51 (m, 2H), 2.30 (m, 2H), 2.32 (s,3H), 2.86 (m, 2H), 4.04 (s, 2H), 4.05 (s, 2H), 4.09 (s, 5H); ¹³C NMR δ29.5, 29.8, 30.2, 30.3, 30.3, 31.8, 67.7, 68.8, 69.2, 90.0, 197.5;FAB-MS obsd 484.2518, calcd exact mass 484.2514; Anal. Calcd forC₂₈H₄₄FeOS: C, 69.40; H, 9.15. Found: C, 69.45; H, 9.07.

1-(4-Ferrocenylphenyl)-2-(4-formylphenyl)acetylene (30)

Samples of 4 (500 mg, 1.75 mmol), 4-iodobenzaldehyde (406 mg, 1.75mmol), CuI (18 mg, 94 μmol) and Pd(PPh₃)₂Cl₂ (8 mg, 11 μmol) were placedin a Schlenk flask. The flask was evacuated for 3 min and then the flaskwas backflushed with argon for 3 min. The process of evacuation andflushing was repeated 3 times. At this point flow rate was increased andthe threaded stopcock was removed. Deaerated THF (5 mL) and DIEA (5.0mL) were added in succession to the flask by gas-tight syringe. Thethreaded stopcock was replaced, the argon flow rate was reduced and theflask was immersed in an oil bath thermostated at 40° C. The reactionwas stopped after 40 h. The mixture was then evaporated and theresulting orange solid was chromatographed (silica, CH₂Cl₂/hexanes,1:1). The second orange band comprising the title compound was collected(579 mg, 84.9%). mp 219-220° C.; ¹H NMR δ 4.10 (s, 5H), 4.42 (s, 2H),4.73 (s, 2H), 7.52 (s, 4H), 7.72, 7.92 (AA′BB′, 4H), 10.07 (s, 1H); ¹³CNMR δ 67.3, 70.3, 70.5, 84.6, 89.4, 94.8, 120.2, 126.6, 130.4, 130.6,132.6, 132.7, 135.9, 141.6, 192.2; EI-MS obsd 390.0696 (M⁺), calcd exactmass 390.0707; Anal. Calcd for C₂₅H₁₈FeO: C, 76.94; H, 4.65. Found: C,76.75; H, 4.68.

5-[4-(S-Acetylthio)phenyl]-15-ferrocenyl-10,20-dimesitylporphyrin (33)

Method A:

Acetonitrile (250 mL) was degassed with a stream of Ar for 10 min.Freshly ground NH₄Cl (1.34 g, 25 mmol) was added and the flask wasplaced in an ice-bath and cooled under Ar. Samples of5-mesityldipyrromethane (Lee et al. (1994) Tetrahedron, 50: 11427-11440;Littler et al. (1999) J. Org. Chem., 64: 1391-1396) (660 mg, 2.50 mmol),4-(S-acetylthio)benzaldehyde 31 (Gryko et al. (1999) J. Org. Chem., 64:8635-8647] (225 mg, 1.25 mmol) and ferrocenecarboxaldehyde (270 mg, 1.25mmol) were added followed by BF₃-etherate (32 μL, 0.25 mmol) and themixture was stirred at 0° C. under Ar. The progress of the reaction wasmonitored by UV-Visible spectroscopy. After 6 h, DDQ (851 mg, 3.75 mmol)was added. The ice-bath was removed and the mixture was stirred at rtfor 1 h. The reaction mixture was evaporated to one-third of its initialvolume and then filtered through a silica pad (CH₂Cl₂/hexanes, 1:1). Thedark solid was subsequently chromatographed (silica, CH₂Cl₂/hexanes,3:7; CH₂Cl₂/hexanes, 5:5). The second green band contained the titleporphyrin together with some impurities. A subsequent chromatographicprocedure did not improve the product purity (119 mg).

Method B:

Samples of 5-mesityldipyrromethane (264 mg, 1.0 mmol),ferrocenecarboxaldehyde (107 mg, 0.50 mmol) and 31 (90 mg, 0.50 mmol)were dissolved in CH₂Cl₂ (100 mL, undistilled) and then TFA (0.137 ml,1.78 mmol) was added slowly over 30 s. The mixture was stirred at rt for30 min, and then DIEA (0.3 mL, 1.8 mmol) and a solution of p-chloranil(370 mg, 1.5 mmol) in THF (20 mL) was added and the mixture was stirredat rt for a further 6 h. Next the reaction mixture was evaporated toone-third of its initial volume and purified as described above toafford 188 mg of the title compound having purity similar to thatobtained via method A. LD-MS obsd 945.6, 961.8 [M⁺+15], 905.4 [M⁺—CH₃CO], impurities 762.7 and 1096.8; FAB-MS obsd 880.2839, calcd exactmass 880.2898 (C₅₆H₄₆N₄OSZnFe); λ_(abs) (CH₂Cl₂) 422, 510, 602 nm.

Zn(II)-5-[4-(S-Acetylthio)phenyl]-15-ferrocenyl-10,20-dimesitylporphyrin(Zn-33)

A solution of porphyrin 33 (100 mg, 0.11 mol) in CH₂Cl₂ (30 mL) wastreated with a solution of Zn(OAc)₂.2H₂O (498 mg, 2.27 mmol) in MeOH (15mL) and the mixture was stirred for 16 h. After metalation was complete(TLC), the reaction mixture was washed with water and dried (Na₂SO₄),filtered, concentrated, and chromatographed (silica, CH₂Cl₂/hexanes,6:4) to give the pure title compound [91 mg, 9.4% (method A) and 37%(method B) from aldehyde 31]. ¹H NMR δ 1.87 (s, 12H), 2.57 (s, 3H), 2.67(s, 6H), 4.24 (s, 5H), 4.79 (s, 2H), 5.52 (s, 2H), 7.31 (s, 6H), 7.77,8.28 (AA′BB′, 4H), 8.7-8.9 (m, 6H), 10.17 (m, 2H); LD-MS obsd 945.6,961.8 [M⁺+15], 905.4 [M⁺ —CH₃CO]; FAB-MS obsd 942.2073, calcd exact mass942.2033 (C₅₆H₄₆N₄OSZnFe); λ_(abs) (CH₂Cl₂) 423, 563, 616 nm.

5-{4-[S—(N-Ethylcarbamoyl)thio]phenyl}-15-(4-ferrocenylphenyl)-10,20-dimesityl-porphyrin(34)

Method A:

Acetonitrile (207 mL) was degassed with a stream of Ar for 10 min.Freshly ground NH₄Cl (1.11 g, 20.7 mmol) was added and the flask wasplaced in an ice-bath and cooled under Ar. Samples of5-mesityldipyrromethane (546 mg, 2.07 mmol), 4-ferrocenylbenzaldehyde 17(300 mg, 1.03 mmol) and aldehyde 32 (216 mg, 1.03 mmol) were addedfollowed by BF₃-etherate (25 μL, 0.209 mmol) and the mixture was stirredat 0° C. under Ar. The progress of the reaction was monitored byUV-Visible spectroscopy. After 5 h, DDQ (705 mg, 3.11 mmol) was added.The ice-bath was removed and the mixture was stirred at rt for 1 h. TEA(28.8 μL, 2.07 mmol) was added and the mixture was chromatographed(silica, CH₂Cl₂/hexanes, 1:1). The dark purple solid was subsequentlychromatographed (silica, CH₂Cl₂/hexanes, 7:3; CH₂Cl₂). The second purpleband (R_(f)=0.54) contained the title porphyrin together with some blueimpurities. A subsequent column chromatography procedure did not improvethe product purity (34 mg).

Method B:

Samples of 5-mesityldipyrromethane (264 mg, 1.0 mmol), 17 (145 mg, 0.50mmol) and 32 (105 mg, 0.50 mmol) were dissolved in CH₂Cl₂ (100 mL,undistilled) and then TFA (0.137 ml, 1.78 mmol) was added slowly over 30s. The mixture was stirred at rt for 30 min, and then DIEA (0.30 mL, 1.8mmol) and a solution of p-chloranil (370 mg, 1.5 mmol) in THF (20 mL)was added and the mixture was stirred at rt for a further 6 h. Next thereaction mixture was concentrated and purified as described above toafford 101 mg. TLC (CH₂Cl₂), R_(f)=0.6; LD-MS obsd 988.6, 917.4 [M⁺—CH₃CH₂NHCO], impurity 850.0; FAB-MS obsd 985.3434, calcd exact mass985.3477 (C₆₃H₅₅N₅OSFe); λ_(abs) (CH₂Cl₂) 419, 517, 553, 593, 648 nm;λ_(abs) 653, 720 nm;

Zinc(II)-5-{4-[S—(N-Ethylcarbamoyl)thio]phenyl}-15-(4-ferrocenylphenyl)-10,20-dimesitylporphyrin(Zn-34)

A solution of 34 (17 mg, 0.017 mmol) in CH₂Cl₂ (15 mL) was treated withZn(OAc)₂.2H₂O (380 mg, 1.73 mmol) in methanol (10 mL) and the mixturewas stirred at rt under argon. TLC analysis (silica, CH₂Cl₂) after 6 hshowed no starting material (expected R_(f)=0.58) and the presence oftwo new components (R_(f)=0.51, R_(f)=0.91). The reaction was stopped byadding 100 mL of satd aq NaHCO₃ and 20 mL of CH₂Cl₂. The aqueoussolution was extracted with CH₂Cl₂. The combined CH₂Cl₂ layers weredried (Na₂SO₄), concentrated and the residue was chromatographed(silica, CH₂Cl₂). The red band was collected and evaporated, affording[16 mg, 3% (method A) and 19% (method B) (from aldehyde 32)]. TLC(silica, CH₂Cl₂) R_(f)=0.51; ¹H NMR 1.30 (t, J=7.0 Hz, 3H), 1.84 (s,12H), 2.64 (s, 6H), 3.4-3.6 (m, 2H), 4.24 (s, 5H), 4.47 (s, 2H), 4.91(s, 2), 5.60 (s, 1H), 7.29 (s, 4H), 7.84, 8.15 (AA′BB′, 4H), 7.92, 8.28(AA′BB′, 4H), 8.7-9.1 (m, 8H); LD-MS obsd 1051.2, 979.0 [M⁺—CH₃CH₂NHCO]; FAB-MS obsd 1047.2625, calcd exact mass 1047.2612(C₆₃H₅₃N₅OSZnFe); λ_(abs) (CH₂Cl₂) 424, 552, 593 nm; λ_(abs) 610, 650nm.

5-[4-(S-Acetylthio)phenyl]-15-{4-[2-(4-ferrocenylphenyl)ethynyl]phenyl}-10,20-dimesitylporphyrin(35)

Samples of 5-mesityldipyrromethane (264 mg, 1.0 mmol), aldehyde 30 (195mg, 0.50 mmol) and aldehyde 32 (105 mg, 0.50 mmol) were dissolved inCH₂Cl₂ (100 mL, undistilled) and then TFA (0.137 ml, 1.78 mmol) wasadded slowly over 30 s. The reaction mixture was stirred at rt for 30min, and then DIEA (0.3 mL, 1.8 mmol) and a solution of p-chloranil (370mg, 1.5 mmol) in THF (20 mL) was added and the mixture was stirred at rtfor a further 6 h. Next the reaction mixture was evaporated to one-thirdof its initial volume and filtered through a silica pad (CH₂Cl₂/hexanes,1:1). Fractions containing the second purple band were collected andchromatographed (silica, CH₂Cl₂/hexanes, 1:1; then CH₂Cl₂) to afford aslightly impure product. A second column (silica, CH₂Cl₂) was performedto obtain 56 mg of pure porphyrin (10.3%). ¹H NMR δ −2.55 (s, 2H); 1.31(t, J=7.2 Hz, 3H), 1.90 (s, 12H), 2.68 (s, 6H), 3.51 (m, 2H), 4.12 (5,H), 4.40 (s, 2H), 4.73 (s, 2H), 5.61 (brt, 1H), 7.34 (s, 6H), 7.56, 7.64(AA′BB′, 4H), 7.9-8.4 (m, 8H), 8.7-9.0 (m, 8H); LD-MS obsd 1089.0,1018.0 [M⁺ —CH₃CH₂NHCO]; FAB-MS obsd 1085.3766, calcd exact mass1085.3790 (C₇₁H₅₉N₅OSFe); λ_(abs) (CH₂Cl₂) 422, 516, 551, 590, 647 nm.

Zn(II)-5-[4-(S-acetylthio)phenyl]-15-{4-[2-(4-ferrocenylphenyl)ethynyl]phenyl}-10,20-dimesitylporphyrin(Zn-35)

A solution of porphyrin 35 (43 mg, 40 μmol) in CH₂Cl₂ (20 mL) wastreated with a solution of Zn(OAc)₂.2H₂O (430 mg, 1.95 mmol) in MeOH (15mL) and the mixture was stirred for 16 h. After metalation was complete,the reaction mixture was washed with water, dried (Na₂SO₄), filtered,concentrated, and chromatographed (silica, CH₂Cl₂) affording a purplesolid (32 mg, 70.3%). ¹H NMR δ 1.30 (t, J=7.2 Hz, 3H), 1.87 (s, 12H),2.67 (s, 6H), 3.4-3.6 (m, 2H), 4.10 (s, 5H), 4.39 (s, 2H), 4.73 (s, 2H),5.57 (brt, 1H), 7.32 (s, 6H), 7.54, 7.62 (AA′BB′, 4H), 7.9-8.4 (m, 8H),8.7-9.0 (m, 8H); LD-MS obsd 1154.0, 1082.7 [M⁺ —CH₃CH₂NHCO]; FAB-MS obsd1147.2724, calcd exact mass 1147.2925 (C₇₁H₅₉N₅OSFe); λ_(abs) (CH₂Cl₂)423, 549 nm.

5-(4-Ferrocenylphenyl)dipyrromethane (36)

Following a general procedure [Lee, C.-H., et al., Tetrahedron 1994, 50,11427-11440; Littler et al. (1999) J. Org. Chem., 64: 1391-1396),pyrrole (3.00 mL, 43.2 mmol) and 4-ferrocenylbenzaldehyde 17 (0.50 g,1.7 mmol) were added to a 25 mL flask and degassed with a stream ofargon. Then TFA (13.0 μL) was added and the mixture was stirred underargon at rt for 10 min and then quenched with 0.1 M NaOH. Ethyl acetatewas then added and the phases were separated. The organic phase waswashed with water, dried (Na₂SO₄), and concentrated to afford an orangeoil. The oil was chromatographed using centrifugal preparative TLC(silica, CH₂Cl₂/hexanes, 1:1) to afford a yellow oil (660 mg, 94.3%). ¹HNMR δ 4.19 (s, 5H), 4.45 (s, 2H), 4.75 (s, 2H), 5.45 (s, 1H), 6.05 (s,2H), 6.30 (m, 2H), 6.71 (m, 2H), 7.22, 7.53 (AA′BB′, J=8.5 Hz, 4H), 7.94(brs, 2H); ¹³C NMR δ 61.3, 67.4, 69.8, 70.5, 86.0, 108.1, 109.1, 118.2,127.1, 129.3, 133.5, 138.6, 140.6; EI-MS obsd 406.1144 (M⁺), calcd exactmass 406.1132 (C₂₅H₂₂N₂Fe).

Zn(II)-5,15-Bis(4-Ferrocenylphenyl)-10-[4-methylphenyl]-20-[4-(S-acetylthio)-phenyl]porphyrin(Zn-37)

Method A:

Acetonitrile (80 mL) was degassed with a stream of Ar for 10 min.Freshly ground NH₄Cl (430 mg, 7.90 mmol) was added, and the flask wasplaced in an ice-bath and cooled under Ar. Samples of 36 (321 mg, 0.79mmol), 4-methylbenzaldehyde (47 μL, 0.40 mmol) and aldehyde 31 (72 mg,0.40 mmol) were added, followed by BF₃-etherate (11 μL, 0.08 mmol), andthe mixture was stirred at 0° C. under Ar. After 6 h DDQ (270 mg, 0.75mmol) was added. The ice-bath was removed and the mixture was stirred atrt for 1 h. TLC revealed a lack of red-fluorescent species, thus CH₂Cl₂(50 mL) was added and the mixture was stirred at rt overnight. Removalof the solvents gave a black solid which was chromatographed (silica,CH₂Cl₂/hexanes, 1:1). The first band collected was chromatographed(silica, CH₂Cl₂/hexanes 7:3, then CH₂Cl₂). The second purple bandcontained the title porphyrin [LD-MS obsd 1075.1; FAB-MS obsd 1070.2435,calcd exact mass 1070.2404 (C₆₇H₅₀N₄Fe₂OS)] together with a significantamount of impurities. Subsequent chromatography procedures with variouseluants did not improve the purity. The mixture (1.5 mg, 1.3 μmol) wasdissolved in CH₂Cl₂ (10 mL) and a solution of Zn(OAc)₂.2H₂O (29.0 mg,130 μmol) in methanol (5 mL) was added and the reaction mixture wasstirred overnight at rt. After metalation was complete, the reactionmixture was washed with water, dried and concentrated. Chromatography(silica, CH₂Cl₂/hexanes) gave 1.5 mg (0.33% from dipyrromethane 36).

Method B:

Acetonitrile (50 mL) was degassed with a stream of Ar for 10 min.Freshly ground NH₄Cl (268 mg, 5.00 mmol) was added, and the flask wasplaced in an ice-bath and cooled under Ar. Samples of 36 (203 mg, 0.50mmol), 4-methylbenzaldehyde (30 μL, 0.25 mmol) and aldehyde 31 (45 mg,0.25 mmol) were added, followed by BF₃-etherate (7 μL, 0.055 mmol), andthe mixture was stirred at 0° C. under Ar. After 6 h, DIEA (10 μL, 0.055mmol) and a solution of p-chloranil (185 mg, 0.75 mmol) in THF (30 mL)was added. The ice-bath was removed and the mixture was stirred at rtovernight. An analogous purification process afforded 29 mg, comprisedof the product and a significant amount of impurities. The mixture wassubsequently metalated with Zn(OAc)₂.2H₂O (595 mg, 2.7 mmol) to obtain8.8 mg (yield 3.1% from dipyrromethane 36) of pure zinc porphyrin. ¹HNMR δ 2.60 (s, 3H), 2.72 (s, 3H), 4.26 (s, 5H), 4.49 (s, 2H), 4.94 (s,2H), 7.5-8.4 (m, 4×AA′BB′, 16H), 8.95-9.10 (m, 8H); LD-MS obsd 1138.7,1153.9 [M⁺+15], 1095.5 [M⁺ —CH₃CO], 966.0; FAB-MS obsd 1132.1526, calcdexact mass 1132.1529 (C₆₇H₄₈N₄Fe₂OS); λ_(abs) (CH₂Cl₂) 421, 551 nm.

Electrochemistry

Both the solution and SAM electrochemical studies were conducted usingthe same instrumentation, techniques, and preparation strategies asdescribed above. The solvent was CH₂Cl₂; tetrabutylammoniumhexafluorophosphate (TBAH, 0.1 M) (Aldrich, recrystallized three timesfrom methanol and dried under vacuum at 110° C.) served as supportingelectrolyte. The potentials reported are vs Ag/Ag⁺; E_(1/2)(FeCp₂/FeCp₂⁺)=0.19 V.

It is understood that the examples and embodiments described herein arefor illustrative purposes only and that various modifications or changesin light thereof will be suggested to persons skilled in the art and areto be included within the spirit and purview of this application andscope of the appended claims. All publications, patents, and patentapplications cited herein are hereby incorporated by reference in theirentirety for all purposes.

1. An apparatus for storing data, said apparatus comprising one or morestorage cells, each storage cell comprising: a fixed electrodeelectrically coupled to a storage medium having a multiplicity ofdifferent and distinguishable oxidation states wherein data is stored insaid oxidation states by the addition or withdrawal of one or moreelectrons from said storage medium via the electrically coupledelectrode.
 2. The apparatus of claim 1, wherein each storage cell isaddressed by at least a single electrode.
 3. The apparatus of claim 1,wherein each storage cell is addressed by two electrodes.
 4. Theapparatus of claim 1, wherein said different and distinguishableoxidation states of said storage medium can be set by a voltagedifference no greater than about 2 volts.
 5. The apparatus of claim 1,wherein said electrode is connected to a voltage source.
 6. Theapparatus of claim 5, wherein said voltage source is the output of anintegrated circuit.
 7. The apparatus of claim 1, wherein said electrodeis connected to a device to read the oxidation state of said storagemedium.
 8. The apparatus of claim 7, wherein said device refreshes theoxidation state of said storage medium after reading said oxidationstate.
 9. The apparatus of claim 7, wherein said device is selected fromthe group consisting of a voltammetric device, an amperometric device,and a potentiometric device.
 10. The apparatus of claim 7, wherein saiddevice is an impedance spectrometer or a sinusoidal voltammeter.
 11. Theapparatus of claim 10, wherein said device provides a Fourier transformof the output signal from said electrode.
 12. The apparatus of any oneof claims 1-6, wherein said storage cell further comprises anelectrolyte.
 13. The apparatus of any one of claims 1-6, wherein saidstorage cell further comprises a dielectric.
 14. The apparatus of claim13, wherein said dielectric is imbedded with counterions.
 15. Theapparatus of claim 14, wherein said dielectric comprises a materialselected from the group consisting of Nafion™, cellulose acetate,polystyrene sulfonate, poly(vinylpyridine), and an electricallyconducting polymer.
 16. The apparatus of claim 13, wherein saiddielectric is juxtaposed to said storage medium.
 17. The apparatus ofany one of claims 1-6, wherein said storage medium and said electrodeare fully encapsulated.